When mapping (or reviewing a map, if you are a Certifier) a calibration course, each endpoint must be described precisely. Ideally, there would be two measurements on an endpoint that is not immediately next to a landmark. If the landmark is away from the curb, there should be two measurements (one from each of two landmarks).
The point of the description and measurement is to enable anyone to replace a lost nail. A description of "about 29 meters south of the stairs" is not anywhere close enough for a calibration course endpoint description. We adjust for temperature when we tape a course, which may move the point ½" or ¼". "About" has no place on a calibration map. Please make sure that all calibration maps have good, precise descriptions of each endpoint, so you or I could take a tape out and replace a lost nail.