This brings us to the third level, that of the device in which the process is to be realized physically The important point here is that, once again, the same algorithm may be implemented in quite different technologies. The child who methodically adds two numbers from right to left, carrying a digit when necessary, may be using the same algorithm that is imple- mented by the wires and transistors of the cash register in the neighbor- hood supermarket, but the physical realization of the algorithm is quite different in these two cases.