I have heard in an audio book:
We go there so often that the chefs and waiters began to set their watches by us.
I am not sure If I write it well. I could not find the expression "set the watch by us" in the dictionary. What does it mean? is it a common expression?
(I am learning English, I am in a small country in Europe)
"You can set your watch to [something or someone]..." is a well-known, though somewhat old-fashioned, expression meaning that [something or someone] is extremely reliable. Sometimes it literally means punctual, but it can be used metaphorically to mean more generally reliable outside of simple punctuality.
I say it's old-fashioned because if you google the phrase, the vast majority of the top results all point to mentions of one particular episode of the TV show "The Simpsons", where Grandpa Simpson (a character portrayed as old-fashioned and conservative) says that a football player with a crew-cut has "a haircut you can set your watch to." That's a deliberately absurd and comedic use of this phrase, and it's deliberately given to the "grandpa" character.
As mechanical watches that have to be regularly adjusted become more and more rare, I expect that this expression will fall further into disuse.
The set their watches by us, here means that the waiters are aware about the timing of arrival of frequently visiting customers referred to by us.
Here specifically, these customers (referred to as us) are frequently visiting the same restaurant periodically at the same time. So, the waiters have become so accustomed about their visiting timings, such that, they always adjust their schedule to accommodate serving them those particular days.
