In this photo the balance is pinned up on a poising tool. The tool rotates both the balance and the 'refrence balance' under it. You have to adjust the length of the spring in order for it to sync up with the refrence balance which is set to the standard frequency of the watch the balance is being prepared for.
Here is the hairspring at the correct length now being studded up to the balance. From this point forward lots of little adjustements need to be made to keep the spring concentric and flat while in the watch. It's the last time you get to work with the spring before it become much more awkard as its placed in between the balance wheel and bridge.
Lastly here is the watch on the timing machine. The three values on the screen represent (from left to right) the daily gain in time, the degrees (in miliseconds) to which the watch is in beat (the balance being correctly aligned to work with the escapement) and lastly the amplitude of the balance, which in itself is a large subject as you need lots of amplitude for the watch to be accurate and sometimes modifications need to be made to increase it..