3 Answers

It could be a blockage made from some sort of nest like a mud dauber or some other local  area nuisance. See short video here.

https://www.youtube.com/watch?v=ksHqjydj5bA

The tension spring solves one problem, but it creates another: friction. The additional friction from the tension spring is responsible link for the drop in balance amplitude you get when you switch a chronograph on, which can be up to 30º. This is acceptable in a properly adjusted watch, but as you can imagine, if you have two chronographs going at once, and both are controlled by a single link balance, you get an amplitude drop link of up to 60º, which is unacceptable.

The story of London Jewelers is a true American Dream. Charles London, a link self-taught clockmaker from Poland, link emigrated to the U.S. in 1923 and quickly established a business at the estates along Long Island's link Gold Coast. He visited each client's home weekly to wind their clocks and offered watch and clock servicing on site. By 1926, Charles had opened a small shop on School Street in Glen Cove, where he performed the watch and clock repairs and eventually began to sell jewelry.