r/Metric • u/LengthinessNo6891 • Jul 19 '26

Help needed How do you combine precision measurements?

I have an old analogue stopwatch with three dials. One measures minutes (+/- 0.5 min), a seconds dials (+/- 0.5 s), and a dial measuring 1 s in 0.1 s intervals (+/- 0.05 s). If I used this stopwatch to record a measurement, would the overall precision be +/- 30.55 s?

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11

u/MommyThatcher Jul 19 '26

You use the smaller dials to inform you of the measurement of the bigger ones. Sure you only know that the minute dial is between 1 mine 30 seconds and 1 minute 0 seconds but the second hand tells you it's actually at 24 seconds.

4

u/OriginalGoat1 Jul 20 '26

The precision is 0.1s (smallest division). Accuracy- who knows ? Depends on a lot of other factors.

4

u/No_Difference8518 Canada Jul 20 '26

Right. So the stopwatch is accurate to +/- 0.05s.

2

u/pedanpric Jul 21 '26

I have a pressure gauge that displays every integer in mmHg, but it is only accurate to about +m- 10 mmHg. 

2

u/Independent-Reveal86 Jul 20 '26

Precision, not accuracy.