Practical investigations
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How do I calculate the percentage error of a stopwatch if the recorded time was 2 hours?
Jenkin writes:
You need to know the minimum time the watch will record. To give you an example, suppose the least time the watch will record is 1 second. You could then argue that the time of 2 hours is +/- 1 second; % error 1/7200 x 100 (= 0.014 %).
But your human error in starting and stopping the watch also has to be considered and is likely to be more significant than any possible error in the watch itself. You need to make a sensible estimate of this, and don’t forget you start and stop the watch, and you will introduce a possible error with each. If your start and stop times were both (say) +/- 2 seconds, the your measured time would be 7200 +/- 4 seconds. Still a very small % error. It would be very different if your measured time was 20 seconds!
Risk assessment
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updated: 14 August 2007
