New watch accuracy and changes

With all new watches, regardless of brand i find it prudent to check accuracy for a couple of weeks.

I'm not particularly interested thereafter.

I picked up a speedy pro 1861 recently. The timing is roughly as followings

Full wind
-4 to -6 after 24 hours, normal active wear

It will typically loose -2 during day and -2 during night.

Low wind (already been running 14-24 hours)
-6 to -10 after 24 hours, normal wear

For the first week it was consistent.

I have let the watch run down 2 or 3 times now and i have left it sitting in the watch box. Each time i do this, i wind it back up and observe time keeping.

The latest is it is currently running at +2 over 24 hours. The first time it has ever run fast. It gained +1 during day and +1 overnight. I must add that the time before it ran down, sat unwound and then re-used, it got faster also, around -1 to -2 over 24 hours. Now its +2.

So clearly during wear it is beginning to change its characteristics of time keeping. The reason i'm raising this is, I purchased a FOIS and a CK in the last 3 years. Both of them displayed exactly the same behaviour. Both of them ran between +6 and +12 when brand new, after 2 to 3 weeks of use they both fell down to between +1 and +6 and have stayed ever since.

Can anyone explain why this happens, i'm curious. From here on forth, i'm hoping for consistency with my latest speedy, just curious as to why it changes a lot initially.

thanks

Thank you Archer. Very happy with all my speedys. Hopefully I will have consistency from now, my other two are very predictable.

Have a good day

FWIW, I’ve been timing my new FOIS for about a week and it has been like yours: it started out by speeding up at a pretty good pace (still within spec overall, mind you), and for the last 36 hours or so it has settled to around +1 second/day.

I’m looking forward to seeing how it behaves over the coming weeks. These tiny machines are just miraculous to me.