The electroencephalograph is often used as a polygraph for recording psychophysiological responses, such as the electrocardiogram, respiration, muscle potentials, and the like. After making a recording of such responses, the investigator frequently wishes to measure large numbers of time intervals. He may wish to know the duration of each successive cycle of respiration or of successive groups of four heartbeats or the time elapsing between the presentation of a stimulus and the beginning of a response. He typically makes the measurements of such intervals with a millimeter "ruler," or scale, placed on the paper chart on which the responses have been recorded.
When making these measurements, the investigator runs into several difficulties. It is not easy for the eye quickly and accurately to pick out the point on the millimeter scale which is exactly opposite, for example, the peak of a given heartbeat recorded on the chart. Fractional parts of
MAYS LL. A Vernier Scale for Measuring Time on Electroencephalogram or Polygraph Chart. AMA Arch NeurPsych. 1957;77(6):659–661. doi:10.1001/archneurpsyc.1957.02330360117014
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