My pocket watch time keeps changing

Hello, A pocket watch I have the time keeps changing on it. I set at 11am this morning and was around a minuet off not to much of a problem. However after a few hours had gone by the time on my watch was around 30 minuets behind and now I've just checked the watch and despite the fact it's 30 minutes behind the minuet hand is 2 minuets head even though I was only off by a minuet when I set it this morning.