St 36 MOVEMENT

[cannon]

The watch is running at +5 sec a day,beat error is 0.6ms don't think it's overbanking as it runs flawless on the bench in the case,I am wondering if the mainspring is not pushing in enough power through the train when it's on my wrist and I'm moving about? Is this a possibility any suggestions will be most appreciated regards Steve 

Well first of all THANKYOU ALL for all your help i have tried everything, i stripped down the movement, polished the fourth wheel pivot,cleaned the mainspring, checked every wheel and pivot,cleaned everything and put it back together,ran great for about one hour then stopped. Took the movement out,blew the balance,hardly moved,looked over the movement from the side and BINGO,the balance was just catching on the centre wheel,couldn't see it from the top,just lifted it ever so slightly using a thin piece of plywood,it's now running perfect into it second day,amplitude is 310,running at plus 4 seconds a day,beat error 0.4ms,pretty damm happy with that, Thanks again for all your help,it's great learning so many ways to fix a watch regards Steve