An aircraft located at some distance from the station would first listen for the identifier, and then when the time delay expired, start a stopwatch.
en.wikipedia.org However, the method of timing a 40-yard dash can affect the accuracy by as much 0.5 seconds (with the manual stopwatch method).
en.wikipedia.org The watch featured shock resistance, meant to survive a fall from 10 metres, 200m water resistance, an alarm function, countdown timer, and stopwatch.
en.wikipedia.org Clearly, the pendulum timings need to be corrected according to how fast or slow the stopwatch was found to be running.
en.wikipedia.org And just for fun there are five permanent tools available via a swipe downward from the top: to-scale 10cm ruler, stopwatch, countdown egg timer, light on/off, and voice recorder.
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