It was a key-driven calculator that was extremely fast because each key adds or subtracts its value to the accumulator as soon as it is pressed. Its skilled operator can enter all of the digits of a number simultaneously, using as many fingers as required, making them sometimes faster to use than electronic calculators. Consequently, in specialized applications, comptometers remained in use in limited numbers into the early 1990s, but with the exception of museum pieces, they have all now been superseded by electronic calculators and computers.

Each row of keys is differentiated from the one above and the one below by a different tactile feel: the even rows have round and raised keys and the odd rows have flat and oblong keys. The keys of the first machines, with their metal rims, are similar to the typewriters keys of the same period. Plastic keys were also introduced very early on but their rows do not have that tactile difference.