[kadoban]

I've used this before for counting. The way I've done it is based on what fingers are touching the desk, or my leg. Reason being, it's kind of awkward holding up/down some finger combinations in the air enough where it's distinct (eg only ring finger up).

So for me it doesn't work too well for communicating numbers, but counting works fine.

[WorldMaker]

Yes, some finger combinations are interesting dexterity challenges (varying among individuals, too), which is why the hysteresis/expectation setting of what's up or down can be important when using it for communication (outside of 132 of course, which is usually pretty obvious). I vaguely recall having at least one drunken conversation with an electrical engineer about what the "voltage equivalent" was for various finger positions might be and what your finger logic gate would need to accept to properly determine finger binary state.