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# precision of stopwatch watch

1. hi i was just wonderin in a physics experiement what is the precision of a stopwatch and would 10 seconds be written as 10.0 or 10.00 seconds?
2. It depends on the watch. And you! What is the smallest division on the scale/readout? Is it 1/10 s, 1/100 s, 1/1000s?
The problem with stop watches is that the readout can often be as "precise" as 1/100 second, but it's not possible to measure the time to that level of certainty, because of your reaction time pressing the button at the start and end of the measurement. This can be of the order of about a tenth of a second at each end of the measurement.
So if you measure a time with a stopwatch, you could have a typical uncertainty of about ± 0.2s.
You would write your measurement of 10 seconds as 10.0 ± 0.2s

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