cubic millimeter

The most precisely metered volumes in engineering are written in this unit. Diesel fuel injection is calibrated in cubic millimetres per stroke: a passenger-car pilot injection is 1 to 2 mm³ per cylinder, the tiny pre-charge that stops a modern diesel knocking at idle, and injector test benches report their delivery maps in nothing else. A cubic millimetre of water weighs one milligram, so those maps are also, silently, fuel-mass maps.

This page carries a second and stranger job. The same symbol, mm³, serves section modulus on this site, the beam property in $\sigma = M/Z$ that turns a bending moment into a stress. A section modulus is not the volume of anything; it is a second moment of area divided by a distance, and its units merely happen to collapse to a length cubed. The catalog keeps the two as separate quantity types precisely so a converter never offers to express a beam property in microlitres, and a reader who arrived here from a structural steel table should follow the section modulus context rather than this one.

Blood work is the third life the definition already names: counts "per mm³" on older lab forms are identical to the modern per-μL figures, so a 1970s reference range needs no conversion at all, only relabelling.