I am using standard test blocks to find the uncertainty of a supermicrometer, which is capable of measuring down to 1/10 of a micron. The issue is that it measures the EXACT same length within a run of even 100 measurements. Understandably, it is suspicious to calculate uncertainty based on data with zero variation; however, the value that it consistently measures is different every time I zero the supermicrometer at a different position. For example, I may get a value of 5.0000 mm repeatedly during one run, zero the supermicrometer, and then get a value of 5.0003 mm repeatedly during the next run.
So the question is, how can I take into consideration variation between runs? Traditionally, one would use a single run to find uncertainty, but I don't think I can do that.