As a watchmaker we have to examine every part of every watch to check for defects. The smallest imperfection in a watch can make a big problem.
If you click on the picture you can see it closer up. This image is taken at 140 power magnification. It may seem like a very small amount of deformation but combined with the deformation in the sliding pinion it is almost impossible to set this watch. The lesson is that you need high magnification and careful inspection to find the defects on watches. Be sure your watchmaker is doing it right.