I demag everything, that is step one.
I use a CHEAP compass to test if the movements have a charge, it's about the size of a quarter.
Simply run the movement past the compass, off to the side of it by about a half inch.
After you demag just run it past the compass again to see if you got the charge out of it.
Probably the cheapest tool in my shop, this compass costs about 10 cents.
A compass that is NOT filled with water seems to work better.
I have bought 2 demagnetizers over the years and I was not happy with them, did not work too well.
Decided to go with something a bit more industrial, not exactly cheap but this puppy rocks!
Author of "Elgin Trench Watches of The Great War"
Author of "Waltham Trench Watches of the Great War"