Hi. Let's say I have data which I have measured. For example I measured a length of an object and the measurment was repeated 5 times. An instrument which I used to measure has an error, value of which I know. My options are to either to just go with the instrument error (probably not, right?) or to calculate the arithmetic mean error from my statistics and go with that. Or I could calculate both and add them together somehow. Which one of these? Thanks!