I have been wondering about this for ages.Can anyone explain why Waltham "left out" a screwdriver slot in the outside edge of the balance wheel recess on 1892 models?It is hard to adjust the meantime screws with the screws so close to the edge...Rockford did it on their's.It would have been an easy machine operation for them to do during manufacture.Maybe to keep the cost down by eliminating one operation? In my personal opinion, the 1892's are about the most beautiful 18s movements ever made!Happy Thanksgiving to all!

Theodore, I am a little puzzled because I never look for a "screwdriver clearance" in the movewment. These jam screws are too delicate for my grubby paws to try adjusting them "in sutu", I fear I would have threaded stumps instead of mean time (MT) screws afterwards!

So it may well be my own ignorance that explains the procedure I follow for adjusting (MT) screws;

When I am timing a watch and want to make an adjustment to the MT screws without breaking the weights or stressing the staff pivots, I remove the Balance cock/wheel assembly, place it upside down on my balance cock tack so that I can carefully hold the wheel and turn the screws with my balance screw chuck tool.

(Please note, I am only showing what it looks like, the chuck is not actually clamped on the screw in pic as I had two to few hands to do all that and take the picture too. )

Another view of the tools;

Another observation . . . my s/n 20,000,108 Model 92 . . .

which as made with 17 jewels for Canadian use (speaks volumes itself) DOES HAVE the adjustment notch in it.

It is just possible that some of the "lower end" model 92's were not so treated.

Thanks, Dave for another great explanation.I have 2 '92 models, a 21J Vanguard and a 17 J Appleton,Tracy & co., both earlier SN's than yours, neither has the notch.They must have started doing it later on.That is a sharp looking watch you have there!