This link has info on how long the hair cycles are on different parts of the body:
BTW, that link is permanently posted as the second entry in the Do-It-Yourself Electrolysis forum.
Just to explain this a little further, the visible hair you see on your face/arm/bodypart isn’t necessarily 1/3 of the hair you have. It might be only 30% of all your hair, or as much as 75% of all the hair you have. What matters more is how much of that hair is in the active growing stage. Because electrolysis and laser only work on hairs that are in the active growing stage. And you can expect to have anywhere from 20-80% of the visible hairs be in active growing stage.
I recently started electro on a new body part. There was a lot of hair to clear but unfortunately for me, only about 20% of it was in active growth. The rest was dead brush, ha. So at any rate we got a good idea of how much hair I do have, now we have to get it as it grows in.
You can tell the stage of the hair by looking at the root. Active growth roots are round black bulbs. Old hairs have a thick white bulb on the end.
One way people try to insure that all their hair is in active growth when they start electrolysis is to shave the area a week or so beforehand. (Whatever you do, don’t wax it! It distorts the follicle’s shape.) But if the area is small or you don’t want to shave it, no sweat. The electro’s needle will get it anyway.