[EricH]

Originally Posted by MrForbes

Just make the numbers so us blind old folks can read them, please?

This. I would also suggest the following test:

If you (Edit: or, preferably, your grandparents) cannot read your robot's numbers from 50 yards out (150 ft), give or take a bit, then you may want to reconsider font, size, or stroke. Why 50 yards? That would be some of the farther scouts who are wishing they'd brought binoculars to read your numbers.