Many wildlife biologists still rely on strip-chart recorders for collecting telemetry information in the field, and modifications that improve the reliability of recording telemetric data and reduce the time required to analyze these data are needed. We observed that 2 identical recorders, which had been geared to run at the same chart speed (5.08 cm/hour), operated at different speeds (4.32 cm/hour and 5.49 cm/hour) and responded differently to declining battery voltage (12.8-12.3 V) over 5- to 15-day recording periods. We describe a simple timer circuit that can be added readily to existing chart recorder systems to designate time on the chart tape. The frequency and duration of timing marks are completely adjustable. A time-marking system enables the biologist to correct for changing chart speed quickly, know the time at which a remote unit may have failed or run out of paper, and greatly facilitates computerized analyses of the strip charts.