Hi, I've been reading about stacking up tolerances. It's the first time in working with them. I understand the gist of it and I've seen a few simple examples however when I move onto my project I keep getting lost as I dont know what and where do they stack and if I should just add them up or Add them up and divide by two? (some of them are holes) Here is the gist of it: A flat PCB (a sheet looking thing with no components) slides into an aluminum block that has a datum feature on the side. the PCB is supposed to stop at that daturm. That datum is on Block A (Black). Once the PCB is up against the stopper, Block B (grey) then drops on top of the PCB with some dowel pins. The PCB mechanical drawing has those two holes as datum features with a tolerance of .003" (.075mm) The thing is, Block B (grey) is mounted onto a big fiber-glass sheet (Let's calle it Block C). Block A and Block B are mounted on the same sheet, and are assembled using screws. My main question is: - Would the tolerance analysis be done on Block C since that's where the alignment between block A and block B are done? or is it done on block A or block C or some sort of combination? and where does the PCB come into play?