Temperature is perhaps the most important factor that affects quartz crystal time
base performance. The quartz crystals used in wrist watch time bases are cut in
such a way as to make them most stable near body temperature. The time base
acts as a thermally stable oscillator while it is on a person’s wrist. Stopwatches,
on the other hand, use quartz crystals that have been cut to be stable at or near
room temperature. If they are used in very hot or very cold environments, the
time base can vary by over 20 parts in 106. Figure 24 shows the accuracy of a
typical stopwatch over a temperature range of 0 °C to 50 °C (32 °F to 122 °F).