ode That YouTube clip shows him marking the hump or firm part of the shaft as he rolls it in the bearings..... typically you would mark the part of the shaft that snaps back off that hump and consistently comes to rest at one spot, the nbp, and install at 9. He thinks he is finding the spine, which he may be, and marks it and places it at 9. That is contrary to what most do who use this type of device.
Exactly. When a shaft is loaded into a spine finder it rotates to the weakest side of the shaft up which is the NBP. It is difficult for me to see if the video is actually showing him marking the spine or NBP. Without letting the shaft come to rest on it's own it is hard to tell. My first spine finder was similar to the one in the video but I had a hose clamp around the tip bearing with a wire that I could hook the bearing to the base with the shaft under load to let it rotate to a resting point. To further confuse you I can't tell if he is using a steel shaft or not. If it is steel you can also throw in "residual shaft bend" which further complicates things. Here is my old NF2 which identifies the Spines, NBPs and a dial gauge that gives a relative flex reading for the shaft and the spines and NBP's. You load a shaft into the rotator board bearings and then bend the shaft tip under the tip bearing. The shafts rotates on it's own to the weakest point on top of the bend. This is an NBP. There is a guide in top near that shaft that I mark the NBP and write down the gauge reading. I then spin the shaft and it may rotate to another NBP which is usually 180° from the other.
And back to the basic question of the markings on your shaft, are the markings the spine or NBP? Here is some good reading from Dave Tutleman who has done tons of research on lots of golf topics including spining. https://www.tutelman.com/golf/ BTW, some shafts have very small spines and can be oriented in any position without any impact on performance. Tutleman suggests shafts with 3cpm or less diff between the spines and NBP can be oriented however.