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Calibration of scientific echo sounders and integrators entails, inter alia, measurement of the dynamic range. This can be done by repeating on-axis measurements of echoes from each of two different standard targets. When a large dynamic range is to be tested, use of a reflector may be convenient. An example is given for which a target strength of roughly 15 dB was desired for use at 38 kHz. The solution: a 12-mm-thick copper disk of 50-cm diameter, is described. Results from its first field applications, where linear operation of a new acoustic system over a 56-dB range was established, are given.