At the tip of every balance wheel pivot sits a little flat ruby jewel called a cap jewel. It’s role is integral in the capped system for reducing friction on balance pivots. When the watch is dial up or dial down the rounded tip of the balance wheel rests on the cap jewel, instead of the shoulder resting on the flat of the hole jewel (as it would with the other pivots.) This is covered with more detail in the post on Shock Resistance and in the post on cap jewels.
The point of this post is to stress the importance of examining cap jewels when servicing a watch.
This little cap jewel has a small imperfection (at the tip of the arrow in the photo). It may seem like a little thing, just a tiny little dimple, but that little dimple increases the amount of friction significantly. I missed this imperfection during disasembly and when I put the watch together the timing results were quite ugly!
I might have thought it was the balance staff but a wise watchmaker at the last AWCI convention taught me that it is easier to check jewels than staffs so I switched the upper jewels with the lower jewels and got the opposite results. I knew it was the jewels. I pulled them out, cleaned them off and that is when I discovered the small indentation in the cap jewel. I replaced the jewel and with the new jewel in place I got the following rates:
And with a little adjustment of the hairspring and regulation I was able to get:
In the world of watchmaking . . . it is the small things that make all the difference. Be sure to carefully examine every component for wear. Little things affect timing, future wear, and your reputation.