the fist step in the selection procedure is to clearly the nature of the quantity that is to be measured. This awareness should include a knowledge of the range of magnitudes and frequencies that the quantity may be expected to exhibit. when the problem has thus been stated, the available transducer principles for measuring the desired quantity must be examined. If one or more transducer principles are cable of producing a satisfactory signal, we must decide whether to use a commercially available transducer or undertake to build the transducer. If commercially manufactured transducers are available at a suitable price, the choice will probably be to purchase one of them.