A chronometer is a clock built to stay extremely exact — not “about the right time,” but right to a tiny part of a second, even after many hours. Scientists use that kind of clock, and sailors once lived by it: at sea, if your clock drifted, you could not tell how far east or west you were, and ships were lost that way. So this is not a fashion watch, not a kitchen timer, and not the stopwatch on a sports watch. It is a serious measuring tool that happens to measure time, and the word still sounds formal and technical. People stretch it a little for any instrument they trust to keep time with almost no error, but the home of the word is science and navigation.