normal to gain time as spring winds down?

[Shaman]

Am putting a new-to-me day-date through some simple checks and have a question/observation. I had this 1984 day-date serviced and must say I am blown away by it's accuracy. It took two days before I could honestly say I was a second off. I wound the watch every day for 40 winds for a week and gained 13 seconds. I let the watch wind down to zero so I can put it in my winder and test the rotor. In the last 48 hours I gained 13 seconds, most of that in the last 24 (still within COSC though). Question/observation is mechanical watches tend to gain time faster as power reserve approaches zero. Does that sound about right? A fully wound watch keeps more consistant time?

[C. Davidson]

Originally Posted by Shaman

Am putting a new-to-me day-date through some simple checks and have a question/observation. I had this 1984 day-date serviced and must say I am blown away by it's accuracy. It took two days before I could honestly say I was a second off. I wound the watch every day for 40 winds for a week and gained 13 seconds. I let the watch wind down to zero so I can put it in my winder and test the rotor. In the last 48 hours I gained 13 seconds, most of that in the last 24 (still within COSC though). Question/observation is mechanical watches tend to gain time faster as power reserve approaches zero. Does that sound about right? A fully wound watch keeps more consistant time?

It is very difficult to wind a watch on a winder alone. Its best to put the watch fully wound on the winder, and this helps it to maintain its power. When you put a watch thats completely dead on the winder, you will get very mixed results, not a good test for any watch since the winder is not giving the watch a full wind.

Your first test of winding your watch every day is a more accurate test of your average daily rate.

And yes, the more power in the watch (aka fully winded mainspring), the more accurate it will be. As the given watch winds down, its rate will be more irratic. Post 24 hours for a COSC watch it should still be giving you good results. Post 40 hours, the results become more and more goofy.

[SLS]

As the mainspring winds down, the watch will tend to gain a little.
Scott

[gregdolley]

Originally Posted by Shaman

Am putting a new-to-me day-date through some simple checks and have a question/observation. I had this 1984 day-date serviced and must say I am blown away by it's accuracy. It took two days before I could honestly say I was a second off. I wound the watch every day for 40 winds for a week and gained 13 seconds. I let the watch wind down to zero so I can put it in my winder and test the rotor. In the last 48 hours I gained 13 seconds, most of that in the last 24 (still within COSC though). Question/observation is mechanical watches tend to gain time faster as power reserve approaches zero. Does that sound about right? A fully wound watch keeps more consistant time?

ALL my watches start to gain time as the power reserve gets low. So your observations sound good.

[GMTJOHNNY]

Agreed. I have found similar results. I still found that my best results were frmo wearing my watch all day, then at night taking it off. I store it face down overnight. It gains seconds "lost" during the day and remains within +/- 2 seconds per month. When I wear my watch to be, and never take it off, it seems to lose more seconds. So, in conclusion, this is fully in line with the above statements that as the spring winds down it gains seconds. Cheers.

[Tools]

On a fully wound watch the mainspring exerts maximum pull on the gear train..... this means that as the pallet fork locks and unlocks, the fork is pushed more forcefully against the jewel at the base of the hairspring causing it to give maximum swing (amplitude). This results in a pretty well known rate... So fully wound equals maximum torque, full balance wheel swing (amplitude), and consistent timekeeping..

If the mainspring is run down, then there is less torque or pull on the gear train, so there is less energy imparted on the balance jewel by the tail of the pallet, and it swings in less of an arc (less amplitude)....... less amplitude means the hairspring is oscillating faster, and locking/unlocking the escapement at a quicker rate..... So, a partially wound mainspring equals less energy at the hairspring, faster swing (less amplitude or oscillation), and a faster watch......

[paranoid new owner]

Can I jump in here and say a big thanks for finally assuaging my fears somewhat? I'm not a big-spending watch-owner but fell for an ExpII at around the time I (for once!) had a little money. But also had a head full of fears about such a famously copied brand. So, having owned cheapie digitals my whole life that stayed pretty well on time I was shocked and worried by my ExpII gaining as much time (measurable daily?!) as it did and have lived with fears that all my cautious prechecking failed me and I wound up (pardon the pun) with a fake. Like others, I thought something 'up there' like a Rolex would have stunning accuracy. I'm beginning to believe I'm wrong and love my (freshly-confidently-genuine) Rolex all over again Thank you, all ya'll - wish I'd found you sooner