The "verifiable competency," in the form of ASQ certification, is subjective at best, and near-worthless at worst, especially as it applies to calibration. As far as I can see, there's nothing in the calibration BOK that deals with the nitty-gritty of calibration of mechanical devices. Work instructions should serve two purposes. The main purpose is the obvious one (to provide instructions for users) but the other one--to establish a standard for performing a task, is just as important, and can't be avoided by having "certified" people.