second hand "sticks" and "jumps"

[stevewood]

Hello,

I was given an 21 jewel automatic divers' watch for Chrtistmas. I notice that the sweeping second hand sometimes "sticks" momentarily then "jumps" in order to "catch up" - usually at around the same place on the face (between the 12 and the 3). - timekeeping does not seem to be affected.

Any ideas about what might cause a problem like this?

Many Thanks.