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diff --git a/src/main/java/org/unitConverter/unit/BaseUnit.java b/src/main/java/org/unitConverter/unit/BaseUnit.java
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+/**
+ * Copyright (C) 2019 Adrien Hopkins
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package org.unitConverter.unit;
+
+import java.util.HashSet;
+import java.util.Objects;
+import java.util.Set;
+
+/**
+ * A unit that other units are defined by.
+ * <p>
+ * Note that BaseUnits <b>must</b> have names and symbols. This is because they
+ * are used for toString code. Therefore, the Optionals provided by
+ * {@link #getPrimaryName} and {@link #getSymbol} will always contain a value.
+ * 
+ * @author Adrien Hopkins
+ * @since 2019-10-16
+ */
+public final class BaseUnit extends Unit {
+	/**
+	 * Gets a base unit from the dimension it measures, its name and its symbol.
+	 * 
+	 * @param dimension dimension measured by this unit
+	 * @param name      name of unit
+	 * @param symbol    symbol of unit
+	 * @return base unit
+	 * @since 2019-10-16
+	 */
+	public static BaseUnit valueOf(final BaseDimension dimension,
+			final String name, final String symbol) {
+		return new BaseUnit(dimension, name, symbol, new HashSet<>());
+	}
+	
+	/**
+	 * Gets a base unit from the dimension it measures, its name and its symbol.
+	 * 
+	 * @param dimension dimension measured by this unit
+	 * @param name      name of unit
+	 * @param symbol    symbol of unit
+	 * @return base unit
+	 * @since 2019-10-21
+	 */
+	public static BaseUnit valueOf(final BaseDimension dimension,
+			final String name, final String symbol, final Set<String> otherNames) {
+		return new BaseUnit(dimension, name, symbol, otherNames);
+	}
+	
+	/**
+	 * The dimension measured by this base unit.
+	 */
+	private final BaseDimension dimension;
+	
+	/**
+	 * Creates the {@code BaseUnit}.
+	 * 
+	 * @param dimension   dimension of unit
+	 * @param primaryName name of unit
+	 * @param symbol      symbol of unit
+	 * @throws NullPointerException if any argument is null
+	 * @since 2019-10-16
+	 */
+	private BaseUnit(final BaseDimension dimension, final String primaryName,
+			final String symbol, final Set<String> otherNames) {
+		super(primaryName, symbol, otherNames);
+		this.dimension = Objects.requireNonNull(dimension,
+				"dimension must not be null.");
+	}
+	
+	/**
+	 * Returns a {@code LinearUnit} with this unit as a base and a conversion
+	 * factor of 1. This operation must be done in order to allow units to be
+	 * created with operations.
+	 * 
+	 * @return this unit as a {@code LinearUnit}
+	 * @since 2019-10-16
+	 */
+	public LinearUnit asLinearUnit() {
+		return LinearUnit.valueOf(this.getBase(), 1);
+	}
+	
+	@Override
+	protected double convertFromBase(final double value) {
+		return value;
+	}
+	
+	@Override
+	protected double convertToBase(final double value) {
+		return value;
+	}
+	
+	/**
+	 * @return dimension
+	 * @since 2019-10-16
+	 */
+	public final BaseDimension getBaseDimension() {
+		return this.dimension;
+	}
+	
+	@Override
+	public String toString() {
+		return this.getPrimaryName().orElse("Unnamed unit")
+				+ (this.getSymbol().isPresent()
+						? String.format(" (%s)", this.getSymbol().get())
+						: "");
+	}
+	
+	@Override
+	public BaseUnit withName(final NameSymbol ns) {
+		Objects.requireNonNull(ns, "ns must not be null.");
+		if (!ns.getPrimaryName().isPresent())
+			throw new IllegalArgumentException(
+					"BaseUnits must have primary names.");
+		if (!ns.getSymbol().isPresent())
+			throw new IllegalArgumentException("BaseUnits must have symbols.");
+		return BaseUnit.valueOf(this.getBaseDimension(),
+				ns.getPrimaryName().get(), ns.getSymbol().get(),
+				ns.getOtherNames());
+	}
+}