Tool watch is a term often used in the world of horology, but its definition is nebulous and murky and potentially controversial—if you are speaking to the wrong person. In simplest terms, a tool watch has at least one function, beyond timekeeping, for which it was designed. A dive watch, for example, is often equipped with a rotating bezel to track elapsed time while under water. A chronograph has one or more sub-registers which can be actuated to like a stopwatch. It may also work in conjunction with a tachymeter scale to calculate speed over distance.