After some dimensional chasing I was able to get what I believe to be a valid overall calculated balance staff length. The bottom pivot jewel of this watch sits in a plate saddle like some of the Waltham’s that I’ve worked on, so calculating that length wasn’t as straight forward as presented in Fried’s book. Anyway… here are the results…
Calculated length to the underside of the top and bottom cap jewels = 0.247”
Actual pivot-to-pivot length=0.2315”
The difference is therefore 0.016”
Sixteen thousandths is a small number and considering that there has to be some measurement error, I’m not sure how much this is really worth.