You are bang on, while the term "vertical drop" isnt in the book its alluded to in 10-23-B.
The first place I read of this term was in a local TGM (ish) instructors book, "The Canadian Move" by Mark Evershead. Not sure if this is his word smithing or not. Though somewhat related much of the book is outside of The Golfing Machine.
But of critical importance when employing this near vertical path of the hands is 1-L-18 as it pertains to plane shifts:
"Changing the Plane Angle has no effect on the Plane Line"
That is to say that you can change the plane angle but make sure you always stay on plane. Confusing I know.
Threaded Mode
