Stabila vials are definitely fixed, and definitely not adjustable. We permanently epoxy and weld them in place. We do not use any springs, screws, rivets, nuts, bolts, etc. The vial is assembled into a plastic housing. The housing is epoxied and welded in place. The accuracy of the level is set. Then it is checked about halfway through the curing cycle. Then, after it is cured, the accuracy is certified. Then the level is packaged and sold. There is no need for a prospective buyer to sort through the stack of levels, looking for the most accurate.