Nice people, really. Textbooks, handouts, guidesheets and the like are offered by well-meaning trainers in this field, taking arithmetic to its ludicrous extreme. Reviewing maintenance logs at a resort pool recently a consultant discovered that the pool's saturation index had been calculated every single day, and minute corrections were performed almost as often. The indicated flow was well within the manufacturer's tolerance, and could not have been confirmed as a non-conformity with the code. Now figure, to make things worse, that the guesstimated depth of the pool's complex bottom could easily be off in either direction by, conservatively, one-half foot.
Cooks make level cups with a straight edge.
Pilots plan flights into assumed winds to the nearest half minute. Weather folks say we've received 21.63 inches of rain so far, and it'll rain again at noon next Wednesday. In an airplane, there's always a magnetic compass and an directional gyroscope in the instrument panel. The gyro, on the other hand, is stable and hair-splittin' precise, to the nearest half degree or so. And it is never more accurate than the original calibration.