The construction and performance of an inexpensive, manually operated, electromechanical trace reader is described. Function generator circuits involving the use of biased diode networks are used to simulate convex and sigmoid calibration graphs by a series of linear approximations. The outputs of these circuits are used to drive a digital voltmeter with print-out. Comparative trials of the conventional manual procedure and the trace reader are reported. A measurement rate of 30 peaks minute–1 and precision of 0·5 per cent. f.s.d. are readily achieved with the trace reader. The system is less demanding on the powers of concentration of the operator, reduces the risk of transcription error and doubles the measurement rate of a single operator.