You can count 0-9 one one hand by simply staring with fist for zero, then raise the fingers in one direction for 1-5, then close them in the SAME direction to get 6-9 back to the fist. Because the raised fingers are on opposite ends of the hand, it's easy to distinguish a 2 from an 8. Meaning you can count from 0 to 99 using both hands. And I'm not being all that efficient. With a mastery of binary, one can go from 0 to 1023 using both hands.