Millimetre

[Sonia]

A lineal measure in the metric system, containing the
thousandth part of a meter; equal to .03937 of an inch. See 3d Meter.

[Jessica]

The measurement penises (or peni) should be measured with so us guys can feel like our dicks are bigger (bigger numbers!). Also more accurate than inches so there.

[Marquetta]

a unit of length that is equal to 0.001 metres