allowance for unoccupied time and for interference may be important for the measurement of machine-controlled operations, but they do not always appear in every computation of standard time. relaxation allowance, on the other hand, has to be taken into account in every computation, whether the job is a simple manual one or a very complex operation requiring the simultaneous control of several machines. a contingency allowance will probably figure quite frequently in the compilation of standard times; it is therefore convenient to consider the contingency allowance and relaxation allowance, so that the sequence of calculation which started with the completion of observations at the workplace may be taken right through to the compilation of standard time.