Fig. 4. The schematic of the system. sinewave into the system. We had the computer running MATLAB store the values output by the adders when this constant signal was input. Because the sample-and-hold and adder circuits are linear, we knew that the stored values would always be the offset's "piece" of the output. In the next phase, the user was told to enter his/her signal plus the offset. By subtracting the stored values of the output of the adders to the offset from the measured output, 100 we effectively removed the influence of the offset. In this way we were able to enter our three frequencies (one at a time, of course), and we were able to input a constant voltage by inputting the fixed offset plus the constant voltage. This system has worked well for us. Over the course of well over a thousand (fairly simple) measurements, we were able to correctly determine the frequency of the input from the compressed signal more than 99% of the time. IEEE Instrumentation & Measurement Magazine April 2020