Added units and dimensions to the design document

13 files changed, 161 insertions, 138 deletions

diff --git a/docs/design.org b/docs/design.org
index 383a707..41713eb 100644
--- a/docs/design.org
+++ b/docs/design.org
@@ -11,8 +11,31 @@
 * Unit System Design
   Any code related to the backend unit system is stored in the ~sevenUnits.unit~ package.
 ** Dimensions
+   Dimensions represent what a unit is measuring, such as length, time, or energy.  Dimensions are represented as an [[*ObjectProduct][ObjectProduct]]<BaseDimension>, where ~BaseDimension~ is a very simple class (its only properties are a name and a symbol) which represents the dimension of a base unit; these base dimensions can be multiplied to create all other Dimensions.
 ** Unit Classes
+   Units are internally represented by the abstract class ~Unit~.  All units have an [[*ObjectProduct][ObjectProduct]]<BaseUnit> (referred to as the base) that they are based on, a dimension (ObjectProduct<BaseDimension>), one or more names and a symbol (these last two bits of data are contained in the ~NameSymbol~ class).  The dimension is calculated from the base unit when needed; the variable is just a cache.  It has two constructors: a package-private one used to make ~BaseUnit~ instances, and a protected one used to make general units (for other subclasses of ~Unit~).  All unit classes are immutable.
+
+   Units also have two conversion functions - one which converts from a value expressed in this unit to its base unit, and another which converts from a value expressed in the base unit to this unit.  In ~Unit~, they are defined as two abstract methods.  This allows you to convert from any unit to any other (as long as they have the same base, i.e. you aren't converting metres to pounds).  To convert from A to B, first convert from A to its base, then convert from the base to B.
+
+   ~BaseUnit~ represents a unit that all other units are defined by.  All of the units used by this system are defined by seven SI ~BaseUnit~ instances (metre, second, kilogram, ampere, kelvin, mole, candela; this is what 7Units is named after) and two non-SI ~BaseUnit~ instances (US dollar and bit).  Because base units are themselves units (and should be able to be used as units), ~BaseUnit~ is a subclass of ~Unit~, using its own package-private constructor.
+
+   However, most units are instances of ~LinearUnit~, another subclass of ~Unit~.  ~LinearUnit~ represents a unit that is /a product of a base unit and a constant called the *conversion factor*/.  Most units you've ever used fall under this definition, the only common exceptions are degrees Celsius and Fahrenheit.  This simplicity allows the ~LinearUnit~ to do many things:
+   - It can implement conversion to and from the base as multiplying and dividing respectively by the conversion factor
+   - You can easily create new units by multiplying or dividing a ~LinearUnit~ by a number (for example, kilometre = metre * 1000).  This can be easily implemented as multiplying this unit's conversion factor by the multiplier and returning a new ~LinearUnit~ with that conversion factor factor.
+   - You can add or subtract two ~LinearUnit~ instances to create a third (as long as they have the same base) by adding or subtracting the conversion factor.
+   - You can multiply or divide any two ~LinearUnit~ instances to create a third by multiplying or dividing the bases and conversion factors.
+   - Note that any operations will return a unit without name(s) or a symbol.  All unit classes have a ~withName~ method that returns a copy of them with different names and/or a different symbol (all of this info is contained in the ~NameSymbol~ class)
+
+   There are a few more classes which play small roles in the unit system:
+   - Unitlike :: A class that is like a unit, but its "value" can be any class.  The only use of this class right now is to implement ~MultiUnit~, a combination of units (like "foot + inch", commonly used in North America for measuring height); its "value" is a list of numbers.
+   - FunctionalUnit :: A convenience class that implements the two conversion functions of ~Unit~ using ~DoubleUnaryOperator~ instances.  This is used internally to implement degrees Celsius and Fahrenheit.  There is also a version of this for ~Unitlike~, ~FunctionalUnitlike~.
+   - UnitValue :: A value expressed as a certain unit (such as "7 inches").  This class is used by the simple unit converter to represent units.  You can convert them between units.  There are also versions of this for ~LinearUnit~ and ~Unitlike~.
+   - Metric :: A static utility class with instances of all of the SI named units, the 9 base dimensions, SI prefixes, some common prefixed units like the kilometre, and a few non-SI units used commonly with them.
+   - BritishImperial :: A static utility class with instances of common units in the British Imperial system (not to be confused with the US Customary system, which is also called "Imperial"; it has the same unit names but the values of a few units are different).  This class and the US Customary is divided into static classes for each dimension, such as ~BritishImperial.Length~.
+   - USCustomary :: A static utility class with instances of common units in the US Customary system (not to be confused with the British Imperial system; it has the same unit names but the values of a few units are different).
 ** Prefixes
+   
+** The Unit Database
 * Utility Classes
   7Units has a few general "utility" classes.  They aren't directly related to units, but are used in the units system.
 ** ObjectProduct
diff --git a/src/main/java/sevenUnits/converterGUI/DefaultPrefixRepetitionRule.java b/src/main/java/sevenUnits/converterGUI/DefaultPrefixRepetitionRule.java
index 835651e..6b6abf0 100644
--- a/src/main/java/sevenUnits/converterGUI/DefaultPrefixRepetitionRule.java
+++ b/src/main/java/sevenUnits/converterGUI/DefaultPrefixRepetitionRule.java
@@ -6,7 +6,7 @@ package sevenUnits.converterGUI;
 import java.util.List;
 import java.util.function.Predicate;
 
-import sevenUnits.unit.SI;
+import sevenUnits.unit.Metric;
 import sevenUnits.unit.UnitPrefix;
 
 /**
@@ -49,7 +49,7 @@ enum DefaultPrefixRepetitionRule implements Predicate<List<UnitPrefix>> {
 			// if the first prefix is non-metric (including binary prefixes),
 			// assume we are using non-metric prefixes
 			// non-metric prefixes are allowed, but can't be repeated.
-			if (!SI.DECIMAL_PREFIXES.contains(prefixes.get(0)))
+			if (!Metric.DECIMAL_PREFIXES.contains(prefixes.get(0)))
 				return NO_REPETITION.test(prefixes);
 			
 			int part = 0; // 0=yotta/yoctos, 1=kilo-zetta/milli-zepto,
@@ -58,7 +58,7 @@ enum DefaultPrefixRepetitionRule implements Predicate<List<UnitPrefix>> {
 			for (final UnitPrefix prefix : prefixes) {
 				// check that the current prefix is metric and appropriately
 				// magnifying/reducing
-				if (!SI.DECIMAL_PREFIXES.contains(prefix))
+				if (!Metric.DECIMAL_PREFIXES.contains(prefix))
 					return false;
 				if (magnifying != prefix.getMultiplier() > 1)
 					return false;
@@ -72,7 +72,7 @@ enum DefaultPrefixRepetitionRule implements Predicate<List<UnitPrefix>> {
 					break;
 				case 1:
 					// after a kilo-zetta, only deka/hecto are valid
-					if (SI.THOUSAND_PREFIXES.contains(prefix))
+					if (Metric.THOUSAND_PREFIXES.contains(prefix))
 						return false;
 					break;
 				case 2:
@@ -81,9 +81,9 @@ enum DefaultPrefixRepetitionRule implements Predicate<List<UnitPrefix>> {
 				}
 				
 				// set part
-				if (SI.YOTTA.equals(prefix) || SI.YOCTO.equals(prefix)) {
+				if (Metric.YOTTA.equals(prefix) || Metric.YOCTO.equals(prefix)) {
 					part = 0;
-				} else if (SI.THOUSAND_PREFIXES.contains(prefix)) {
+				} else if (Metric.THOUSAND_PREFIXES.contains(prefix)) {
 					part = 1;
 				} else {
 					part = 2;
diff --git a/src/main/java/sevenUnits/converterGUI/SevenUnitsGUI.java b/src/main/java/sevenUnits/converterGUI/SevenUnitsGUI.java
index e1eb2f4..bfd5974 100644
--- a/src/main/java/sevenUnits/converterGUI/SevenUnitsGUI.java
+++ b/src/main/java/sevenUnits/converterGUI/SevenUnitsGUI.java
@@ -70,7 +70,7 @@ import sevenUnits.unit.BritishImperial;
 import sevenUnits.unit.LinearUnit;
 import sevenUnits.unit.LinearUnitValue;
 import sevenUnits.unit.NameSymbol;
-import sevenUnits.unit.SI;
+import sevenUnits.unit.Metric;
 import sevenUnits.unit.Unit;
 import sevenUnits.unit.UnitDatabase;
 import sevenUnits.unit.UnitPrefix;
@@ -110,25 +110,25 @@ final class SevenUnitsGUI {
 		 * @since v0.2.0
 		 */
 		private static void addDefaults(final UnitDatabase database) {
-			database.addUnit("metre", SI.METRE);
-			database.addUnit("kilogram", SI.KILOGRAM);
-			database.addUnit("gram", SI.KILOGRAM.dividedBy(1000));
-			database.addUnit("second", SI.SECOND);
-			database.addUnit("ampere", SI.AMPERE);
-			database.addUnit("kelvin", SI.KELVIN);
-			database.addUnit("mole", SI.MOLE);
-			database.addUnit("candela", SI.CANDELA);
-			database.addUnit("bit", SI.BIT);
-			database.addUnit("unit", SI.ONE);
+			database.addUnit("metre", Metric.METRE);
+			database.addUnit("kilogram", Metric.KILOGRAM);
+			database.addUnit("gram", Metric.KILOGRAM.dividedBy(1000));
+			database.addUnit("second", Metric.SECOND);
+			database.addUnit("ampere", Metric.AMPERE);
+			database.addUnit("kelvin", Metric.KELVIN);
+			database.addUnit("mole", Metric.MOLE);
+			database.addUnit("candela", Metric.CANDELA);
+			database.addUnit("bit", Metric.BIT);
+			database.addUnit("unit", Metric.ONE);
 			// nonlinear units - must be loaded manually
-			database.addUnit("tempCelsius", SI.CELSIUS);
+			database.addUnit("tempCelsius", Metric.CELSIUS);
 			database.addUnit("tempFahrenheit", BritishImperial.FAHRENHEIT);
 			
 			// load initial dimensions
-			database.addDimension("LENGTH", SI.Dimensions.LENGTH);
-			database.addDimension("MASS", SI.Dimensions.MASS);
-			database.addDimension("TIME", SI.Dimensions.TIME);
-			database.addDimension("TEMPERATURE", SI.Dimensions.TEMPERATURE);
+			database.addDimension("LENGTH", Metric.Dimensions.LENGTH);
+			database.addDimension("MASS", Metric.Dimensions.MASS);
+			database.addDimension("TIME", Metric.Dimensions.TIME);
+			database.addDimension("TEMPERATURE", Metric.Dimensions.TEMPERATURE);
 		}
 		
 		/**
diff --git a/src/main/java/sevenUnits/unit/BritishImperial.java b/src/main/java/sevenUnits/unit/BritishImperial.java
index 63da7f0..81a3f2a 100644
--- a/src/main/java/sevenUnits/unit/BritishImperial.java
+++ b/src/main/java/sevenUnits/unit/BritishImperial.java
@@ -48,7 +48,7 @@ public final class BritishImperial {
 		/**
 		 * According to the International Yard and Pound of 1959, a yard is defined as exactly 0.9144 metres.
 		 */
-		public static final LinearUnit YARD = SI.METRE.times(0.9144);
+		public static final LinearUnit YARD = Metric.METRE.times(0.9144);
 		public static final LinearUnit FOOT = YARD.dividedBy(3);
 		public static final LinearUnit INCH = FOOT.dividedBy(12);
 		public static final LinearUnit THOU = INCH.dividedBy(1000);
@@ -57,7 +57,7 @@ public final class BritishImperial {
 		public static final LinearUnit MILE = FURLONG.times(8);
 		public static final LinearUnit LEAGUE = MILE.times(3);
 
-		public static final LinearUnit NAUTICAL_MILE = SI.METRE.times(1852);
+		public static final LinearUnit NAUTICAL_MILE = Metric.METRE.times(1852);
 		public static final LinearUnit CABLE = NAUTICAL_MILE.dividedBy(10);
 		public static final LinearUnit FATHOM = CABLE.dividedBy(100);
 
@@ -72,7 +72,7 @@ public final class BritishImperial {
 	 * @since 2019-11-08
 	 */
 	public static final class Mass {
-		public static final LinearUnit POUND = SI.GRAM.times(453.59237);
+		public static final LinearUnit POUND = Metric.GRAM.times(453.59237);
 		public static final LinearUnit OUNCE = POUND.dividedBy(16);
 		public static final LinearUnit DRACHM = POUND.dividedBy(256);
 		public static final LinearUnit GRAIN = POUND.dividedBy(7000);
@@ -80,7 +80,7 @@ public final class BritishImperial {
 		public static final LinearUnit QUARTER = STONE.times(2);
 		public static final LinearUnit HUNDREDWEIGHT = QUARTER.times(4);
 		public static final LinearUnit LONG_TON = HUNDREDWEIGHT.times(20);
-		public static final LinearUnit SLUG = SI.KILOGRAM.times(14.59390294);
+		public static final LinearUnit SLUG = Metric.KILOGRAM.times(14.59390294);
 	}
 
 	/**
@@ -90,7 +90,7 @@ public final class BritishImperial {
 	 * @since 2019-11-08
 	 */
 	public static final class Volume {
-		public static final LinearUnit FLUID_OUNCE = SI.LITRE.withPrefix(SI.MILLI).times(28.4130625);
+		public static final LinearUnit FLUID_OUNCE = Metric.LITRE.withPrefix(Metric.MILLI).times(28.4130625);
 		public static final LinearUnit GILL = FLUID_OUNCE.times(5);
 		public static final LinearUnit PINT = FLUID_OUNCE.times(20);
 		public static final LinearUnit QUART = PINT.times(2);
@@ -104,13 +104,13 @@ public final class BritishImperial {
 		public static final LinearUnit ACRE_FOOT = Area.ACRE.times(Length.FOOT);
 	}
 
-	public static final LinearUnit OUNCE_FORCE = Mass.OUNCE.times(SI.Constants.EARTH_GRAVITY);
-	public static final LinearUnit POUND_FORCE = Mass.POUND.times(SI.Constants.EARTH_GRAVITY);
+	public static final LinearUnit OUNCE_FORCE = Mass.OUNCE.times(Metric.Constants.EARTH_GRAVITY);
+	public static final LinearUnit POUND_FORCE = Mass.POUND.times(Metric.Constants.EARTH_GRAVITY);
 
-	public static final LinearUnit BRITISH_THERMAL_UNIT = SI.JOULE.times(1055.06);
-	public static final LinearUnit CALORIE = SI.JOULE.times(4.184);
-	public static final LinearUnit KILOCALORIE = SI.JOULE.times(4184);
+	public static final LinearUnit BRITISH_THERMAL_UNIT = Metric.JOULE.times(1055.06);
+	public static final LinearUnit CALORIE = Metric.JOULE.times(4.184);
+	public static final LinearUnit KILOCALORIE = Metric.JOULE.times(4184);
 
-	public static final Unit FAHRENHEIT = Unit.fromConversionFunctions(SI.KELVIN.getBase(),
+	public static final Unit FAHRENHEIT = Unit.fromConversionFunctions(Metric.KELVIN.getBase(),
 			tempK -> tempK * 1.8 - 459.67, tempF -> (tempF + 459.67) / 1.8);
 }
diff --git a/src/main/java/sevenUnits/unit/LinearUnitValue.java b/src/main/java/sevenUnits/unit/LinearUnitValue.java
index ffb9271..a36d568 100644
--- a/src/main/java/sevenUnits/unit/LinearUnitValue.java
+++ b/src/main/java/sevenUnits/unit/LinearUnitValue.java
@@ -32,7 +32,7 @@ import sevenUnits.utils.UncertainDouble;
  * @since 2020-07-26
  */
 public final class LinearUnitValue {
-	public static final LinearUnitValue ONE = getExact(SI.ONE, 1);
+	public static final LinearUnitValue ONE = getExact(Metric.ONE, 1);
 	
 	/**
 	 * Gets an exact {@code LinearUnitValue}
diff --git a/src/main/java/sevenUnits/unit/SI.java b/src/main/java/sevenUnits/unit/Metric.java
index 278fb5e..3c4d291 100644
--- a/src/main/java/sevenUnits/unit/SI.java
+++ b/src/main/java/sevenUnits/unit/Metric.java
@@ -36,7 +36,7 @@ import sevenUnits.utils.ObjectProduct;
  * @author Adrien Hopkins
  * @since 2019-10-16
  */
-public final class SI {
+public final class Metric {
 	/// dimensions used by SI units
 	// base dimensions, as BaseDimensions
 	public static final class BaseDimensions {
@@ -402,57 +402,57 @@ public final class SI {
 			.withName(NameSymbol.of("exbi", "Ei"));
 	
 	// a few prefixed units
-	public static final LinearUnit MICROMETRE = SI.METRE.withPrefix(SI.MICRO);
-	public static final LinearUnit MILLIMETRE = SI.METRE.withPrefix(SI.MILLI);
-	public static final LinearUnit KILOMETRE = SI.METRE.withPrefix(SI.KILO);
-	public static final LinearUnit MEGAMETRE = SI.METRE.withPrefix(SI.MEGA);
+	public static final LinearUnit MICROMETRE = Metric.METRE.withPrefix(Metric.MICRO);
+	public static final LinearUnit MILLIMETRE = Metric.METRE.withPrefix(Metric.MILLI);
+	public static final LinearUnit KILOMETRE = Metric.METRE.withPrefix(Metric.KILO);
+	public static final LinearUnit MEGAMETRE = Metric.METRE.withPrefix(Metric.MEGA);
 	
-	public static final LinearUnit MICROLITRE = SI.LITRE.withPrefix(SI.MICRO);
-	public static final LinearUnit MILLILITRE = SI.LITRE.withPrefix(SI.MILLI);
-	public static final LinearUnit KILOLITRE = SI.LITRE.withPrefix(SI.KILO);
-	public static final LinearUnit MEGALITRE = SI.LITRE.withPrefix(SI.MEGA);
+	public static final LinearUnit MICROLITRE = Metric.LITRE.withPrefix(Metric.MICRO);
+	public static final LinearUnit MILLILITRE = Metric.LITRE.withPrefix(Metric.MILLI);
+	public static final LinearUnit KILOLITRE = Metric.LITRE.withPrefix(Metric.KILO);
+	public static final LinearUnit MEGALITRE = Metric.LITRE.withPrefix(Metric.MEGA);
 	
-	public static final LinearUnit MICROSECOND = SI.SECOND.withPrefix(SI.MICRO);
-	public static final LinearUnit MILLISECOND = SI.SECOND.withPrefix(SI.MILLI);
-	public static final LinearUnit KILOSECOND = SI.SECOND.withPrefix(SI.KILO);
-	public static final LinearUnit MEGASECOND = SI.SECOND.withPrefix(SI.MEGA);
+	public static final LinearUnit MICROSECOND = Metric.SECOND.withPrefix(Metric.MICRO);
+	public static final LinearUnit MILLISECOND = Metric.SECOND.withPrefix(Metric.MILLI);
+	public static final LinearUnit KILOSECOND = Metric.SECOND.withPrefix(Metric.KILO);
+	public static final LinearUnit MEGASECOND = Metric.SECOND.withPrefix(Metric.MEGA);
 	
-	public static final LinearUnit MICROGRAM = SI.GRAM.withPrefix(SI.MICRO);
-	public static final LinearUnit MILLIGRAM = SI.GRAM.withPrefix(SI.MILLI);
-	public static final LinearUnit MEGAGRAM = SI.GRAM.withPrefix(SI.MEGA);
+	public static final LinearUnit MICROGRAM = Metric.GRAM.withPrefix(Metric.MICRO);
+	public static final LinearUnit MILLIGRAM = Metric.GRAM.withPrefix(Metric.MILLI);
+	public static final LinearUnit MEGAGRAM = Metric.GRAM.withPrefix(Metric.MEGA);
 	
-	public static final LinearUnit MICRONEWTON = SI.NEWTON.withPrefix(SI.MICRO);
-	public static final LinearUnit MILLINEWTON = SI.NEWTON.withPrefix(SI.MILLI);
-	public static final LinearUnit KILONEWTON = SI.NEWTON.withPrefix(SI.KILO);
-	public static final LinearUnit MEGANEWTON = SI.NEWTON.withPrefix(SI.MEGA);
+	public static final LinearUnit MICRONEWTON = Metric.NEWTON.withPrefix(Metric.MICRO);
+	public static final LinearUnit MILLINEWTON = Metric.NEWTON.withPrefix(Metric.MILLI);
+	public static final LinearUnit KILONEWTON = Metric.NEWTON.withPrefix(Metric.KILO);
+	public static final LinearUnit MEGANEWTON = Metric.NEWTON.withPrefix(Metric.MEGA);
 	
-	public static final LinearUnit MICROJOULE = SI.JOULE.withPrefix(SI.MICRO);
-	public static final LinearUnit MILLIJOULE = SI.JOULE.withPrefix(SI.MILLI);
-	public static final LinearUnit KILOJOULE = SI.JOULE.withPrefix(SI.KILO);
-	public static final LinearUnit MEGAJOULE = SI.JOULE.withPrefix(SI.MEGA);
+	public static final LinearUnit MICROJOULE = Metric.JOULE.withPrefix(Metric.MICRO);
+	public static final LinearUnit MILLIJOULE = Metric.JOULE.withPrefix(Metric.MILLI);
+	public static final LinearUnit KILOJOULE = Metric.JOULE.withPrefix(Metric.KILO);
+	public static final LinearUnit MEGAJOULE = Metric.JOULE.withPrefix(Metric.MEGA);
 	
-	public static final LinearUnit MICROWATT = SI.WATT.withPrefix(SI.MICRO);
-	public static final LinearUnit MILLIWATT = SI.WATT.withPrefix(SI.MILLI);
-	public static final LinearUnit KILOWATT = SI.WATT.withPrefix(SI.KILO);
-	public static final LinearUnit MEGAWATT = SI.WATT.withPrefix(SI.MEGA);
+	public static final LinearUnit MICROWATT = Metric.WATT.withPrefix(Metric.MICRO);
+	public static final LinearUnit MILLIWATT = Metric.WATT.withPrefix(Metric.MILLI);
+	public static final LinearUnit KILOWATT = Metric.WATT.withPrefix(Metric.KILO);
+	public static final LinearUnit MEGAWATT = Metric.WATT.withPrefix(Metric.MEGA);
 	
-	public static final LinearUnit MICROCOULOMB = SI.COULOMB
-			.withPrefix(SI.MICRO);
-	public static final LinearUnit MILLICOULOMB = SI.COULOMB
-			.withPrefix(SI.MILLI);
-	public static final LinearUnit KILOCOULOMB = SI.COULOMB.withPrefix(SI.KILO);
-	public static final LinearUnit MEGACOULOMB = SI.COULOMB.withPrefix(SI.MEGA);
+	public static final LinearUnit MICROCOULOMB = Metric.COULOMB
+			.withPrefix(Metric.MICRO);
+	public static final LinearUnit MILLICOULOMB = Metric.COULOMB
+			.withPrefix(Metric.MILLI);
+	public static final LinearUnit KILOCOULOMB = Metric.COULOMB.withPrefix(Metric.KILO);
+	public static final LinearUnit MEGACOULOMB = Metric.COULOMB.withPrefix(Metric.MEGA);
 	
-	public static final LinearUnit MICROAMPERE = SI.AMPERE.withPrefix(SI.MICRO);
-	public static final LinearUnit MILLIAMPERE = SI.AMPERE.withPrefix(SI.MILLI);
+	public static final LinearUnit MICROAMPERE = Metric.AMPERE.withPrefix(Metric.MICRO);
+	public static final LinearUnit MILLIAMPERE = Metric.AMPERE.withPrefix(Metric.MILLI);
 	
-	public static final LinearUnit MICROVOLT = SI.VOLT.withPrefix(SI.MICRO);
-	public static final LinearUnit MILLIVOLT = SI.VOLT.withPrefix(SI.MILLI);
-	public static final LinearUnit KILOVOLT = SI.VOLT.withPrefix(SI.KILO);
-	public static final LinearUnit MEGAVOLT = SI.VOLT.withPrefix(SI.MEGA);
+	public static final LinearUnit MICROVOLT = Metric.VOLT.withPrefix(Metric.MICRO);
+	public static final LinearUnit MILLIVOLT = Metric.VOLT.withPrefix(Metric.MILLI);
+	public static final LinearUnit KILOVOLT = Metric.VOLT.withPrefix(Metric.KILO);
+	public static final LinearUnit MEGAVOLT = Metric.VOLT.withPrefix(Metric.MEGA);
 	
-	public static final LinearUnit KILOOHM = SI.OHM.withPrefix(SI.KILO);
-	public static final LinearUnit MEGAOHM = SI.OHM.withPrefix(SI.MEGA);
+	public static final LinearUnit KILOOHM = Metric.OHM.withPrefix(Metric.KILO);
+	public static final LinearUnit MEGAOHM = Metric.OHM.withPrefix(Metric.MEGA);
 	
 	// sets of prefixes
 	public static final Set<UnitPrefix> ALL_PREFIXES = Set.of(DEKA, HECTO, KILO,
@@ -473,7 +473,7 @@ public final class SI {
 			MILLI, MICRO, NANO, PICO, FEMTO, ATTO, ZEPTO, YOCTO);
 	
 	// You may NOT get SI instances!
-	private SI() {
+	private Metric() {
 		throw new AssertionError();
 	}
 }
diff --git a/src/main/java/sevenUnits/unit/USCustomary.java b/src/main/java/sevenUnits/unit/USCustomary.java
index 76356c0..459071f 100644
--- a/src/main/java/sevenUnits/unit/USCustomary.java
+++ b/src/main/java/sevenUnits/unit/USCustomary.java
@@ -52,7 +52,7 @@ public final class USCustomary {
 		public static final LinearUnit YARD = BritishImperial.Length.YARD;
 		public static final LinearUnit MILE = BritishImperial.Length.MILE;
 
-		public static final LinearUnit SURVEY_FOOT = SI.METRE.times(1200.0 / 3937.0);
+		public static final LinearUnit SURVEY_FOOT = Metric.METRE.times(1200.0 / 3937.0);
 		public static final LinearUnit SURVEY_LINK = SURVEY_FOOT.times(33.0 / 50.0);
 		public static final LinearUnit SURVEY_ROD = SURVEY_FOOT.times(16.5);
 		public static final LinearUnit SURVEY_CHAIN = SURVEY_ROD.times(4);
@@ -97,7 +97,7 @@ public final class USCustomary {
 		public static final LinearUnit CUBIC_YARD = Length.YARD.toExponent(3);
 		public static final LinearUnit ACRE_FOOT = Area.ACRE.times(Length.FOOT);
 
-		public static final LinearUnit MINIM = SI.LITRE.withPrefix(SI.MICRO).times(61.611519921875);
+		public static final LinearUnit MINIM = Metric.LITRE.withPrefix(Metric.MICRO).times(61.611519921875);
 		public static final LinearUnit FLUID_DRAM = MINIM.times(60);
 		public static final LinearUnit TEASPOON = MINIM.times(80);
 		public static final LinearUnit TABLESPOON = TEASPOON.times(3);
@@ -112,7 +112,7 @@ public final class USCustomary {
 		public static final LinearUnit OIL_BARREL = GALLON.times(42);
 		public static final LinearUnit HOGSHEAD = GALLON.times(63);
 
-		public static final LinearUnit DRY_PINT = SI.LITRE.times(0.5506104713575);
+		public static final LinearUnit DRY_PINT = Metric.LITRE.times(0.5506104713575);
 		public static final LinearUnit DRY_QUART = DRY_PINT.times(2);
 		public static final LinearUnit DRY_GALLON = DRY_QUART.times(4);
 		public static final LinearUnit PECK = DRY_GALLON.times(2);
@@ -128,7 +128,7 @@ public final class USCustomary {
 	public static final LinearUnit KILOCALORIE = BritishImperial.KILOCALORIE;
 	public static final LinearUnit FOOT_POUND = POUND_FORCE.times(Length.FOOT);
 
-	public static final LinearUnit HORSEPOWER = Length.FOOT.times(POUND_FORCE).dividedBy(SI.MINUTE).times(33000);
+	public static final LinearUnit HORSEPOWER = Length.FOOT.times(POUND_FORCE).dividedBy(Metric.MINUTE).times(33000);
 	public static final LinearUnit POUND_PER_SQUARE_INCH = POUND_FORCE.dividedBy(Length.INCH.toExponent(2));
 
 	public static final Unit FAHRENHEIT = BritishImperial.FAHRENHEIT;
diff --git a/src/main/java/sevenUnits/unit/Unit.java b/src/main/java/sevenUnits/unit/Unit.java
index 8fcacb8..58b4e10 100644
--- a/src/main/java/sevenUnits/unit/Unit.java
+++ b/src/main/java/sevenUnits/unit/Unit.java
@@ -117,7 +117,7 @@ public abstract class Unit implements Nameable {
 	 * @since 2019-10-16
 	 * @throws NullPointerException if unitBase or ns is null
 	 */
-	Unit(ObjectProduct<BaseUnit> unitBase, NameSymbol ns) {
+	protected Unit(ObjectProduct<BaseUnit> unitBase, NameSymbol ns) {
 		this.unitBase = Objects.requireNonNull(unitBase,
 				"unitBase may not be null");
 		this.nameSymbol = Objects.requireNonNull(ns, "ns may not be null");
@@ -192,7 +192,7 @@ public abstract class Unit implements Nameable {
 	 * 
 	 * @implSpec This method is used by {@link #convertTo}, and its behaviour
 	 *           affects the behaviour of {@code convertTo}.
-	 * 
+	 * 				
 	 * @param value value expressed in <b>base</b> unit
 	 * @return value expressed in <b>this</b> unit
 	 * @since 2018-12-22
@@ -208,7 +208,7 @@ public abstract class Unit implements Nameable {
 	 *           {@code other.convertFromBase(this.convertToBase(value))}.
 	 *           Therefore, overriding either of those methods will change the
 	 *           output of this method.
-	 * 
+	 * 				
 	 * @param other unit to convert to
 	 * @param value value to convert
 	 * @return converted value
@@ -235,7 +235,7 @@ public abstract class Unit implements Nameable {
 	 *           {@code other.convertFromBase(this.convertToBase(value))}.
 	 *           Therefore, overriding either of those methods will change the
 	 *           output of this method.
-	 * 				
+	 * 
 	 * @param other unitlike form to convert to
 	 * @param value value to convert
 	 * @param <W>   type of value to convert to
@@ -270,7 +270,7 @@ public abstract class Unit implements Nameable {
 	 * 
 	 * @implSpec This method is used by {@link #convertTo}, and its behaviour
 	 *           affects the behaviour of {@code convertTo}.
-	 * 
+	 * 				
 	 * @param value value expressed in <b>this</b> unit
 	 * @return value expressed in <b>base</b> unit
 	 * @since 2018-12-22
@@ -342,7 +342,7 @@ public abstract class Unit implements Nameable {
 		
 		// second condition - check that
 		for (final BaseUnit b : linear.getBase().getBaseSet()) {
-			if (!SI.BaseUnits.BASE_UNITS.contains(b))
+			if (!Metric.BaseUnits.BASE_UNITS.contains(b))
 				return false;
 		}
 		
diff --git a/src/main/java/sevenUnits/unit/UnitDatabase.java b/src/main/java/sevenUnits/unit/UnitDatabase.java
index a40f000..b45d9cf 100644
--- a/src/main/java/sevenUnits/unit/UnitDatabase.java
+++ b/src/main/java/sevenUnits/unit/UnitDatabase.java
@@ -1116,7 +1116,7 @@ public final class UnitDatabase {
 	private static final LinearUnit exponentiateUnits(final LinearUnit base,
 			final LinearUnit exponentUnit) {
 		// exponent function - first check if o2 is a number,
-		if (exponentUnit.getBase().equals(SI.ONE.getBase())) {
+		if (exponentUnit.getBase().equals(Metric.ONE.getBase())) {
 			// then check if it is an integer,
 			final double exponent = exponentUnit.getConversionFactor();
 			if (DecimalComparison.equals(exponent % 1, 0))
@@ -1142,7 +1142,7 @@ public final class UnitDatabase {
 	private static final LinearUnitValue exponentiateUnitValues(
 			final LinearUnitValue base, final LinearUnitValue exponentValue) {
 		// exponent function - first check if o2 is a number,
-		if (exponentValue.canConvertTo(SI.ONE)) {
+		if (exponentValue.canConvertTo(Metric.ONE)) {
 			// then check if it is an integer,
 			final double exponent = exponentValue.getValueExact();
 			if (DecimalComparison.equals(exponent % 1, 0))
@@ -1676,7 +1676,7 @@ public final class UnitDatabase {
 			final BigDecimal number = new BigDecimal(name);
 			
 			final double uncertainty = Math.pow(10, -number.scale());
-			return LinearUnitValue.of(SI.ONE,
+			return LinearUnitValue.of(Metric.ONE,
 					UncertainDouble.of(number.doubleValue(), uncertainty));
 		} catch (final NumberFormatException e) {
 			return LinearUnitValue.getExact(this.getLinearUnit(name), 1);
@@ -1786,7 +1786,7 @@ public final class UnitDatabase {
 	public Unit getUnit(final String name) {
 		try {
 			final double value = Double.parseDouble(name);
-			return SI.ONE.times(value);
+			return Metric.ONE.times(value);
 		} catch (final NumberFormatException e) {
 			final Unit unit = this.units.get(name);
 			if (unit == null)
diff --git a/src/test/java/sevenUnits/unit/MultiUnitTest.java b/src/test/java/sevenUnits/unit/MultiUnitTest.java
index 82722af..d632118 100644
--- a/src/test/java/sevenUnits/unit/MultiUnitTest.java
+++ b/src/test/java/sevenUnits/unit/MultiUnitTest.java
@@ -27,7 +27,7 @@ import org.junit.jupiter.api.Test;
 
 import sevenUnits.unit.BritishImperial;
 import sevenUnits.unit.MultiUnit;
-import sevenUnits.unit.SI;
+import sevenUnits.unit.Metric;
 
 /**
  * Tests related to the {@code MultiUnit}.
@@ -42,7 +42,7 @@ class MultiUnitTest {
 		final MultiUnit footInch = MultiUnit.of(BritishImperial.Length.FOOT,
 				BritishImperial.Length.INCH);
 		
-		assertEquals(1702.0, footInch.convertTo(SI.METRE.withPrefix(SI.MILLI),
+		assertEquals(1702.0, footInch.convertTo(Metric.METRE.withPrefix(Metric.MILLI),
 				Arrays.asList(5.0, 7.0)), 1.0);
 		
 		for (int i = 0; i < 1000; i++) {
@@ -50,7 +50,7 @@ class MultiUnitTest {
 			final double inches = rng.nextDouble() * 12;
 			final double millimetres = feet * 304.8 + inches * 25.4;
 			
-			final List<Double> feetAndInches = SI.METRE.withPrefix(SI.MILLI)
+			final List<Double> feetAndInches = Metric.METRE.withPrefix(Metric.MILLI)
 					.convertTo(footInch, millimetres);
 			assertEquals(feet, feetAndInches.get(0), 1e-10);
 			assertEquals(inches, feetAndInches.get(1), 1e-10);
diff --git a/src/test/java/sevenUnits/unit/UnitDatabaseTest.java b/src/test/java/sevenUnits/unit/UnitDatabaseTest.java
index c706b5c..1d5e503 100644
--- a/src/test/java/sevenUnits/unit/UnitDatabaseTest.java
+++ b/src/test/java/sevenUnits/unit/UnitDatabaseTest.java
@@ -33,7 +33,7 @@ import org.junit.jupiter.api.Test;
 
 import sevenUnits.unit.LinearUnit;
 import sevenUnits.unit.NameSymbol;
-import sevenUnits.unit.SI;
+import sevenUnits.unit.Metric;
 import sevenUnits.unit.Unit;
 import sevenUnits.unit.UnitDatabase;
 import sevenUnits.unit.UnitPrefix;
@@ -48,18 +48,18 @@ import sevenUnits.unit.UnitPrefix;
  */
 class UnitDatabaseTest {
 	// some linear units and one nonlinear
-	private static final Unit U = SI.METRE;
-	private static final Unit V = SI.KILOGRAM;
-	private static final Unit W = SI.SECOND;
+	private static final Unit U = Metric.METRE;
+	private static final Unit V = Metric.KILOGRAM;
+	private static final Unit W = Metric.SECOND;
 	
 	// used for testing expressions
 	// J = U^2 * V / W^2
-	private static final LinearUnit J = SI.KILOGRAM.times(SI.METRE.toExponent(2))
-			.dividedBy(SI.SECOND.toExponent(2));
-	private static final LinearUnit K = SI.KELVIN;
+	private static final LinearUnit J = Metric.KILOGRAM.times(Metric.METRE.toExponent(2))
+			.dividedBy(Metric.SECOND.toExponent(2));
+	private static final LinearUnit K = Metric.KELVIN;
 	
 	private static final Unit NONLINEAR = Unit
-			.fromConversionFunctions(SI.METRE.getBase(), o -> o + 1, o -> o - 1);
+			.fromConversionFunctions(Metric.METRE.getBase(), o -> o + 1, o -> o - 1);
 	
 	// make the prefix values prime so I can tell which multiplications were made
 	private static final UnitPrefix A = UnitPrefix.valueOf(2)
diff --git a/src/test/java/sevenUnits/unit/UnitTest.java b/src/test/java/sevenUnits/unit/UnitTest.java
index bad5a31..a980054 100644
--- a/src/test/java/sevenUnits/unit/UnitTest.java
+++ b/src/test/java/sevenUnits/unit/UnitTest.java
@@ -29,7 +29,7 @@ import org.junit.jupiter.api.Test;
 import sevenUnits.unit.LinearUnit;
 import sevenUnits.unit.LinearUnitValue;
 import sevenUnits.unit.NameSymbol;
-import sevenUnits.unit.SI;
+import sevenUnits.unit.Metric;
 import sevenUnits.unit.Unit;
 import sevenUnits.unit.UnitValue;
 import sevenUnits.utils.DecimalComparison;
@@ -48,19 +48,19 @@ class UnitTest {
 	
 	@Test
 	public void testAdditionAndSubtraction() {
-		final LinearUnit inch = SI.METRE.times(0.0254)
+		final LinearUnit inch = Metric.METRE.times(0.0254)
 				.withName(NameSymbol.of("inch", "in"));
-		final LinearUnit foot = SI.METRE.times(0.3048)
+		final LinearUnit foot = Metric.METRE.times(0.3048)
 				.withName(NameSymbol.of("foot", "ft"));
 		
-		assertEquals(inch.plus(foot), SI.METRE.times(0.3302));
-		assertEquals(foot.minus(inch), SI.METRE.times(0.2794));
+		assertEquals(inch.plus(foot), Metric.METRE.times(0.3302));
+		assertEquals(foot.minus(inch), Metric.METRE.times(0.2794));
 		
 		// test with LinearUnitValue
-		final LinearUnitValue value1 = LinearUnitValue.getExact(SI.METRE, 15);
+		final LinearUnitValue value1 = LinearUnitValue.getExact(Metric.METRE, 15);
 		final LinearUnitValue value2 = LinearUnitValue.getExact(foot, 120);
-		final LinearUnitValue value3 = LinearUnitValue.getExact(SI.METRE, 0.5);
-		final LinearUnitValue value4 = LinearUnitValue.getExact(SI.KILOGRAM, 60);
+		final LinearUnitValue value3 = LinearUnitValue.getExact(Metric.METRE, 0.5);
+		final LinearUnitValue value4 = LinearUnitValue.getExact(Metric.KILOGRAM, 60);
 		
 		// make sure addition is done correctly
 		assertEquals(51.576, value1.plus(value2).getValueExact(), 0.001);
@@ -70,8 +70,8 @@ class UnitTest {
 		
 		// make sure addition uses the correct unit, and is still associative
 		// (ignoring floating-point rounding errors)
-		assertEquals(SI.METRE, value1.plus(value2).getUnit());
-		assertEquals(SI.METRE, value1.plus(value2).plus(value3).getUnit());
+		assertEquals(Metric.METRE, value1.plus(value2).getUnit());
+		assertEquals(Metric.METRE, value1.plus(value2).plus(value3).getUnit());
 		assertEquals(foot, value2.plus(value1).getUnit());
 		assertTrue(value1.plus(value2).equals(value2.plus(value1), true));
 		
@@ -81,7 +81,7 @@ class UnitTest {
 	
 	@Test
 	public void testConversion() {
-		final LinearUnit metre = SI.METRE;
+		final LinearUnit metre = Metric.METRE;
 		final Unit inch = metre.times(0.0254);
 		
 		final UnitValue value = UnitValue.of(inch, 75);
@@ -97,7 +97,7 @@ class UnitTest {
 			final double expected = testValue * conversionFactor;
 			
 			// test
-			final Unit unit = SI.METRE.times(conversionFactor);
+			final Unit unit = Metric.METRE.times(conversionFactor);
 			final double actual = unit.convertToBase(testValue);
 			
 			assertEquals(actual, expected,
@@ -107,17 +107,17 @@ class UnitTest {
 	
 	@Test
 	public void testEquals() {
-		final LinearUnit metre = SI.METRE;
-		final Unit meter = SI.BaseUnits.METRE.asLinearUnit();
+		final LinearUnit metre = Metric.METRE;
+		final Unit meter = Metric.BaseUnits.METRE.asLinearUnit();
 		
 		assertEquals(metre, meter);
 	}
 	
 	@Test
 	public void testIsMetric() {
-		final Unit metre = SI.METRE;
-		final Unit megasecond = SI.SECOND.withPrefix(SI.MEGA);
-		final Unit hour = SI.HOUR;
+		final Unit metre = Metric.METRE;
+		final Unit megasecond = Metric.SECOND.withPrefix(Metric.MEGA);
+		final Unit hour = Metric.HOUR;
 		
 		assertTrue(metre.isMetric());
 		assertTrue(megasecond.isMetric());
@@ -127,26 +127,26 @@ class UnitTest {
 	@Test
 	public void testMultiplicationAndDivision() {
 		// test unit-times-unit multiplication
-		final LinearUnit generatedJoule = SI.KILOGRAM
-				.times(SI.METRE.toExponent(2)).dividedBy(SI.SECOND.toExponent(2));
-		final LinearUnit actualJoule = SI.JOULE;
+		final LinearUnit generatedJoule = Metric.KILOGRAM
+				.times(Metric.METRE.toExponent(2)).dividedBy(Metric.SECOND.toExponent(2));
+		final LinearUnit actualJoule = Metric.JOULE;
 		
 		assertEquals(generatedJoule, actualJoule);
 		
 		// test multiplication by conversion factors
-		final LinearUnit kilometre = SI.METRE.times(1000);
-		final LinearUnit hour = SI.SECOND.times(3600);
+		final LinearUnit kilometre = Metric.METRE.times(1000);
+		final LinearUnit hour = Metric.SECOND.times(3600);
 		final LinearUnit generatedKPH = kilometre.dividedBy(hour);
 		
-		final LinearUnit actualKPH = SI.METRE.dividedBy(SI.SECOND).dividedBy(3.6);
+		final LinearUnit actualKPH = Metric.METRE.dividedBy(Metric.SECOND).dividedBy(3.6);
 		
 		assertEquals(generatedKPH, actualKPH);
 	}
 	
 	@Test
 	public void testPrefixes() {
-		final LinearUnit generatedKilometre = SI.METRE.withPrefix(SI.KILO);
-		final LinearUnit actualKilometre = SI.METRE.times(1000);
+		final LinearUnit generatedKilometre = Metric.METRE.withPrefix(Metric.KILO);
+		final LinearUnit actualKilometre = Metric.METRE.times(1000);
 		
 		assertEquals(generatedKilometre, actualKilometre);
 	}
diff --git a/src/test/java/sevenUnits/utils/ObjectProductTest.java b/src/test/java/sevenUnits/utils/ObjectProductTest.java
index 32a8c78..13fd7ec 100644
--- a/src/test/java/sevenUnits/utils/ObjectProductTest.java
+++ b/src/test/java/sevenUnits/utils/ObjectProductTest.java
@@ -18,18 +18,18 @@ package sevenUnits.utils;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
-import static sevenUnits.unit.SI.Dimensions.AREA;
-import static sevenUnits.unit.SI.Dimensions.ENERGY;
-import static sevenUnits.unit.SI.Dimensions.LENGTH;
-import static sevenUnits.unit.SI.Dimensions.MASS;
-import static sevenUnits.unit.SI.Dimensions.MASS_DENSITY;
-import static sevenUnits.unit.SI.Dimensions.QUANTITY;
-import static sevenUnits.unit.SI.Dimensions.TIME;
-import static sevenUnits.unit.SI.Dimensions.VOLUME;
+import static sevenUnits.unit.Metric.Dimensions.AREA;
+import static sevenUnits.unit.Metric.Dimensions.ENERGY;
+import static sevenUnits.unit.Metric.Dimensions.LENGTH;
+import static sevenUnits.unit.Metric.Dimensions.MASS;
+import static sevenUnits.unit.Metric.Dimensions.MASS_DENSITY;
+import static sevenUnits.unit.Metric.Dimensions.QUANTITY;
+import static sevenUnits.unit.Metric.Dimensions.TIME;
+import static sevenUnits.unit.Metric.Dimensions.VOLUME;
 
 import org.junit.jupiter.api.Test;
 
-import sevenUnits.unit.SI;
+import sevenUnits.unit.Metric;
 import sevenUnits.utils.ObjectProduct;
 
 /**
@@ -60,8 +60,8 @@ class ObjectProductTest {
 	 */
 	@Test
 	public void testExponents() {
-		assertEquals(1, LENGTH.getExponent(SI.BaseDimensions.LENGTH));
-		assertEquals(3, VOLUME.getExponent(SI.BaseDimensions.LENGTH));
+		assertEquals(1, LENGTH.getExponent(Metric.BaseDimensions.LENGTH));
+		assertEquals(3, VOLUME.getExponent(Metric.BaseDimensions.LENGTH));
 	}
 
 	/**