Useless measurements

I found this interesting tidbit in an article about strange units of measurement at Wikipedia:

Attoparsec

A nonstandard unit of length is the attoparsec. It comes in disguise and even has a proper symbol, apc. It is, however, rarely used in the real world.

Parsecs are used in astronomy to measure enormous interstellar distances; a parsec is approximately 3.26 light-years or 3.085×10¹⁶ m. Combining it with the "atto" prefix yields attoparsec, a conveniently human-scaled unit of 3.085 centimeters (about 1 7/32 inches) that has no obvious practical use.

Interestingly, 1 attoparsec/microfortnight is nearly 1 inch/second (the actual figure is 1.0043 inch per second or approximately 2.55 cm/s); see mathematical coincidence for a list of similar factoids.