Elgin Grade 291

In the past someone must have either lost or striped the screw in the balance cock that hold the hairspring stud in place.

There's a great big screw in there, looks like a dial foot screw.

The "beat" was way off on this one. A watch is said to be "out of beat" when the idle, centered position of the balance wheel is not centered in the pallet folk. As a result, the wheel turns more to one side than the other, wasting power. You can actually hear this in the pattern of ticking without much difficultly if you get used to it.

The fix is to rotate the hairspring collet a tiny bit until the balance wheel is even.

This is Elgin's grade 291, 16 size, 7 jewels, made about 1907.