Development of a new sensor is driven by the need for a new measurement which in turn is driven by the need for new understanding of some phenomenon. The process of bringing a new sensor on line, validating it, and gaining confidence in its behavior is one familiar to the authors but bears telling. The principal author offers the partly told story of SCIMP, RiNo, BASS, and MAVS to illustrate this process. And, finally, the example of a conversion of a trusted sensor to one with a new controller is presented as a test case. The purpose is to instruct through practical example. In later stages, as in many successful developments, there was a commercial outcome that was both inspiring and frustrating. But it is another lesson in instrument development that should be instructive to engineering practitioners.