How do i calculate percentage uncertainty in physics experiment involving time measurements( using stopwatch)?

for example the two times noted for a trolley to slide down a ramp is 18.23 and 18.15. How r we supposed to calculate % uncertainty in time(t).How do i calculate percentage uncertainty in physics experiment involving time measurements( using stopwatch)?
Average is 18.19



error1 is (23-19)/18.19 = +0.22%

error2 is (19-15)/18.19 = 鈥?.22%



So the error is 卤0.22%



.How do i calculate percentage uncertainty in physics experiment involving time measurements( using stopwatch)?
see if this helps



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