A missing link in the evolution of the cumulative recorder.

A recently recovered cumulative recorder provides a missing link in the evolution of the cumulative recorder from a modified kymograph to a reliably operating, scientifically and commercially successful instrument. The recorder, the only physical evidence of such an early precommercial cumulative recorder yet found, was sent to Keio University in Tokyo, Japan, in 1952 at the behest of B. F. Skinner at Harvard University. Last used in research in the late 1960s, the cumulative recorder remained locked in a storage room until 2007, when it was found again. A historical context for the recorder is followed by a description of the recorder and a comparison between it and the commercially successful Gerbrands Model C-1 recorder. Labeled the Keio recorder, it is a testament to Skinner's persistence in developing a reliable means of quantifying the behavior of living organisms in real time.