Elgin Grade 307 Mainspring

[RyMoeller]

Well here's my second call for help in as many days!

Today I'm disassembling an Elgin size 18 pocket watch from circa 1904.  The movement is a grade 307 and it is wound tight as as a drum but does not run.  The balance moves freely so I know that's not the problem but before I can disassemble the movement and check out its constituent parts I need to relieve the tension from the mainspring... and I can't figure out how to let it down. 

Since the answer is probably right in front of my I'll add the disclaimer that this is my first American pocket watch repair. 

I've attached some pictures which might illustrate the problem.  Thanks in advance for your input!

[oldhippy]

I found this on another forum for you.

Place it into a movement holder so that both the pinhole and the winding mechanism are unobstructed by the movement holder. Insert a bench key into the winding square and add a bit of tension like you are trying to wind the watch. Push a small pin into the hole. The pin will push & release the click. Let the bench key SLOWLY revolve to let down the spring tension.

I prefer to hold the key securely and only allow it to rotate a half-turn before letting the click re-engage. Then reposition my fingers and let it down another half-turn. This helps to control the spring release better in my opinion. The possibility of uncontrolled let-down is possible if you accidentally let the bench key revolve too fast and it gets away from you. This can lead to damaged parts (usually the click or gear teeth) because you may let go and allow the click to try & re-engage the gear teeth at warp speed. There WILL BE sparks if you let this happen

[RyMoeller]

Thanks @oldhippy, that worked perfectly!