Nowhere does it say that you are expected to calibrate it yourself. It says that if you drop it on concrete numerous times over the years and find that it slips, you have the potential to calibrate it yourself as opposed to throwing it away and buying a new one, as I've had to do with two hardened Starrets that vibrated off the table, hit the floor and were never square again.
One piece or multiple pieces, metal moves. It moves less than wood tends to, but it is very, very, very far from anything approaching absolute dimensional stability.
Some peoples' senses of entitlement obviously never change shape. It's too bad no one can make anything useful out of those.