the first time I saw one was on the Zeno deep diver 500m watch

(click to expand if you wish), it is impossible to measure 100m ( to read the speed in Km/h) speed if you cannot 0 the moment you start the 100m.
I have seen others though (cannot remember the brands) after this
in the case of the Zeno, well, probably they repurposed a case which was meant for…
Why would a watch without a chrono function have a tachymeter bezel?