Finger music

What may be the most remarkable about overtone singing is that it unites some very fundamental elements of speech (phonetics), music (intervals) and ... mathematics: each prime number incarnates a new tonal function through the harmonic series. The three fields share a common and very deep source which we may contact through our practice.
One of the oldest ways to indicate tonal functions is by hand and fingers (the guidonian hand etc.). And fingers have always been used to indicate numbers (a digit may be numerical or anatomical!).

Octaves are actually mirrored in the arithmetic series 1-2-4-8-16-... so it is obvious to find a finger counting system which may bridge the numbers and the tonal functions. The most interesting in my view would be to utilize the binary counting, where each digit position is exactly the 1-2-4-... (whereas the the positions of our common 10-digit system are 1-10-100-1.000-...)

In practice it can be used by choir leaders to indicate which harmonic should be amplified, and for establishing awareness in personal practice... developing a harmonic finger language.
One hand can indicate numbers from 0 to 31 which should be sufficient for most overtone singers (and those who need wider frames don't need the fingers). This also gives the choir leader the opportunity to indicate two different harmonics for two different voice groups within one choir.