warning or message when zeros are due to rounding

quick idea I wanted to throw out there -- a stopgap option for avoiding false zeros (in the sense that people see a zero and think it is genuine 0 rather than a small number). Idea is maybe we just throw a small warning / tag when all of the values are showing 0, like "note: all values are showing up as zero, possibly due to rounding. try adjusting the UOMs for the numerator and denominator"):