There are books on how to use an abacus, but basically all it does is
add and subtract, the rest you have to do in your head. Essentially,
this is a proof by induction that a computer is more powerful than an
abacus, since a computer program can contain an abacus. (But then
again, you can simulate a computer within a computer, so what does that
show). Actually, with a real abacus, one can move more than one row at
a time with 10 fingers. But on the other hand, a real abacus does not
have the current sum displayed as an integer.