What is the primary function of a watch?

isn't time a man- invented thing according to the position of the sun, stars and moon in te sky? still I don't know how they got to count it in, like earths rotation, in 360⁰ formation having hours minutes and seconds, even microseconds and nanoseconds? my brother answered '' because it's flat''. is his conspiracy theorism facts? lol commenting for my achievement, sorry.

Watches were preceded by clocks.

I use my phone to tell me the time

I'm not good at telling the time