We are doing an experiment to measure velocity using the ticker-tape timer which runs on a 50 Hz a.c. 12 V power supply. I am in Ireland. So the time interval between each pair of dots is 0.02 s. But is there an uncertainty on this number ? Surely it's not exactly 0.02. I can't seem to find info on this anywhere online.

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    $\begingroup$ suggest you post this on the Electrical Engineering. Lots of experts on AC power over there. $\endgroup$ – niels nielsen Nov 8 '18 at 8:07
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    $\begingroup$ This is an example of a (possible) systematic error i.e. you have no way of knowing whether the tape is running fast or slow. In general systematic errors are hard to estimate. $\endgroup$ – John Rennie Nov 8 '18 at 8:09
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    $\begingroup$ Have a look at the article Accuracy and stability of the 50 Hz mains frequency. $\endgroup$ – Farcher Nov 8 '18 at 8:09

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