Once in a while I have run across a balance wheel that has popped out of its mount, probably from being dropped. These are relatively easy to get back in place, but the hard part is pre-loading the balance wheel spring. These springs are about as thick as a human hair, and must be installed with the appropriate amount of tension. The only way I've found to get the tension right is by trial and error. The clock highlighted in the photo had such a problem. I started out by tensioning the spring with only one winding, then kept increasing the tension until the clock once again kept time correctly. Then I oiled it, and it has worked fine ever since.