Hi all! I'm currently doing an experiment using a compound pendulum trying to determine the value of g. I have a problem with my uncertainties: Error in period T: The period is measured with the use of a photo-gate of accuracy +/- 0.0001s. For each height i did 20 measurements from which i calculated average period and from the standard deviation I have the standard error of mean. However due to the fact that I made so many measurements the standard error of mean sometimes appears to be smaller than the actual precision of the photo-gate (for example +/- 0.00007s). What should I do in this case? I'm guessing I somehow need to combine these uncertainties? I have another question concerning the heights. I firstly had to measure the length of the whole pendulum to find the centre of mass being in the middle. Then I mark the center of mass and measure different heights up to the edge of clamp (this all using a meter stick). Then I measure the distance between edge of clamp and axis of rotation using vernier caliper. Overall I guess it goes like this (correct me if I'm wrong) Uncertainty of meter stick (with the help of magnifying glass) is 1/3mm so +/- 0,3mm. And since I use this uncertainty twice (not sure if center of mass is exactly where marked) AND then when measuring distance to edge of clamp -this gives me +/- 0,6mm and I need to combine this with the uncertainty in the distance on clamp which is +/-0,05mm. So it is sqrt(0,6^2+0,05^2)? Thank you in advance for all the help. PS. If you're not sure please don't reply as I don't want to get more confused than I am.