Hey paul, good idea to mark the escape wheel, I have an idea of checking all the teeth on the escape wheel, tell me what you guys think, I will put up some pics and hope they come thru. using a thin pc. of aluminum i cut it square and scribed 2 lines with a razor blade to mark a center, drilled a hole the size of the arbor, made some reference lines ( it doesnt matter exactly where) and turned the escape wheel using only one point of reference and then checking where the other teeth ended up. I noticed a slight variation of distance from one to the other on this escape wheel, I think combining your idea of having a mark on it would tell the truth 
