Can we say 'your watch has gained/lost 10 minutes? What is the normal way to say this when a watch or clock is slow/fast, and we want to mention the amount of time to show how much slow'fast it is?
I was just thinking that although the fact that is is running slow or running fast is important so that you know it's not accurate, the amount of time it's gained or lost seems unimportant since it will change. That is, if it's running fast, 10 minutes now might be 20 tomorrow.
I think you'll hear more people say "My watch seems to be running fast" than "My watch has gained 10 minutes."
(Not a commentary on the how correct the answer is -- just on how likely you are to need to use it.)
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
I don't know whether this is personal, or normal BrE.
Since answering the question (above), I have realised that I haven't said this about my watch for years. Since batteries replaced clockwork, watches have seemed to keep pretty good time.