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diff --git a/src/org/unitConverter/unit/Unit.java b/src/org/unitConverter/unit/Unit.java
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+++ b/src/org/unitConverter/unit/Unit.java
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+/**
+ * Copyright (C) 2018 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.Objects;
+
+import org.unitConverter.dimension.UnitDimension;
+
+/**
+ * A unit that has an associated base unit, and can convert a value expressed in it to and from that base.
+ * 
+ * @author Adrien Hopkins
+ * @since 2018-12-22
+ * @since v0.1.0
+ */
+public interface Unit {
+	/**
+	 * Checks if a value expressed in this unit can be converted to a value expressed in {@code other}
+	 * 
+	 * @param other
+	 *            unit to test with
+	 * @return true if the units are compatible
+	 * @since 2019-01-13
+	 * @since v0.1.0
+	 */
+	default boolean canConvertTo(final Unit other) {
+		return Objects.equals(this.getBase(), other.getBase());
+	}
+
+	/**
+	 * Converts from a value expressed in this unit's base unit to a value expressed in this unit.
+	 * <p>
+	 * This must be the inverse of {@code convertToBase}, so {@code convertFromBase(convertToBase(value))} must be equal
+	 * to {@code value} for any value, ignoring precision loss by roundoff error.
+	 * </p>
+	 * <p>
+	 * If this unit <i>is</i> a base unit, this method should return {@code value}.
+	 * </p>
+	 * 
+	 * @param value
+	 *            value expressed in <b>base</b> unit
+	 * @return value expressed in <b>this</b> unit
+	 * @since 2018-12-22
+	 * @since v0.1.0
+	 */
+	double convertFromBase(double value);
+
+	/**
+	 * Converts from a value expressed in this unit to a value expressed in this unit's base unit.
+	 * <p>
+	 * This must be the inverse of {@code convertFromBase}, so {@code convertToBase(convertFromBase(value))} must be
+	 * equal to {@code value} for any value, ignoring precision loss by roundoff error.
+	 * </p>
+	 * <p>
+	 * If this unit <i>is</i> a base unit, this method should return {@code value}.
+	 * </p>
+	 * 
+	 * @param value
+	 *            value expressed in <b>this</b> unit
+	 * @return value expressed in <b>base</b> unit
+	 * @since 2018-12-22
+	 * @since v0.1.0
+	 */
+	double convertToBase(double value);
+
+	/**
+	 * <p>
+	 * Returns the base unit associated with this unit.
+	 * </p>
+	 * <p>
+	 * The dimension of this unit must be equal to the dimension of the returned unit.
+	 * </p>
+	 * <p>
+	 * If this unit <i>is</i> a base unit, this method should return this unit.\
+	 * </p>
+	 * 
+	 * @return base unit associated with this unit
+	 * @since 2018-12-22
+	 * @since v0.1.0
+	 */
+	BaseUnit getBase();
+
+	/**
+	 * @return dimension measured by this unit
+	 * @since 2018-12-22
+	 * @since v0.1.0
+	 */
+	UnitDimension getDimension();
+
+	/**
+	 * @return system that this unit is a part of
+	 * @since 2018-12-23
+	 * @since v0.1.0
+	 */
+	UnitSystem getSystem();
+}