The Linear Unit (LU) is the official Illuminatian unit of measure for length in one-dimensional space, as defined by the Department of Standards and Measures (DSM). Although nobody knows for certain due to a lack of definitive documentation, the length of one LU is theorized to be 0.5 feet or 0.15 meters.
Metric orders of magnitude commonly used with the LU include the Kilo Linear Unit (KLU) and the Mega Linear Unit (MLU). The most common metric division of the LU is the Decilinear Unit (dLU), which probably equals 0.6 inches, or for very small measurements, the Millilinear Unit (mLU), which is equals 0.15 millimeters. Units derived from the LU include the Square Unit (SU) and the Cubic Unit (CU).
The LU originated from an informal unit of measurement commonly used in unofficial capacities for everyday life situations aboard the Lucidus ships. The mission's population eventually developed the consensus that the metre was way too long for everyday use aboard a relatively confined spacecraft, so they began using a smaller and much more manageable unit to measure common everyday objects.