Re^2: My favorite model of computation is ...

[marinersk]

A simple technique I picked up somewhere permits counting to 99 on the hands -- left hand is the tens digit, right hand is the units digit, and the thumb counts for 5 fingers.

[SuicideJunkie]

This is my system too. It also works very well for tallying two different counts that occur simultaneously, if they're in the range of 0-9.

Or in a pinch, -9-+9 or 0-19, using memory (short term) or hand inversion (long terms storage) for the extra bit.