A unit of linear measure. A Rubis is 1/7 of a micron. 7 Rubis equals 1 micron. The plural of Rubis is Rubis. An extremely fine unit of measure used by precision lensmakers.
Baird: That Curve is off 3.5 microns.
Steve: Microns?! You hack, that is off 24 Rubis! We only work to the tightest tolerance here! Get your shit together!