A system, method, and computer readable medium for usage billing of one or more hosted applications serving one or more clients. An index having semantic index key terms from one or more documents is maintained. A differentiator is configured to receive the intermediate output values from the calculation network and to generate a decimated output value at an output sample rate in which the output sample rate has a non-integer factor with respect to the input sample rate. The electrical storage device becomes charged through a charging device from the external power source.