In most 3D printers (especially affordable home FDM printer) beside the temperature of the nozzle and the heat-bed nothing is measured at all.
Not even the position of the print-head relative to the print-bed. (Well, to be precise, this position is “measured to be zero” exactly once per print via homing at the end-stop switches.) Average 3D printers work blindly, pretty oblivious of what they area actually doing. In cheap 3D printing it’s simple “steering” (aka “open loop control”). Information only flows into and not out of the system. One hopes that all commands that are given are executed exactly as given. If there is just one mistake then the “mental” model of the printers state that one has in the steering microprocessor does not match the printers state in reality any-more, and a horrible mess is likely to ensue. E.g. crashes, missed steps, printing mid air leading to string spaghetti, or exploding printers (just kidding). dissertation writing services