Spine & Flo
We put the shaft in a Neufinder and find the softest axis of the shaft, this is called N1 which refers to the natural bend plane of the shaft which is the spot the shaft wants to snap to when it's placed under load. Once we find N1, we'll mark a line over some painters tape and this is the spot that should be aligned at the target.
Then we'll clamp the butt of the shaft and mount a laser to the tip and twang it along the intended target line and observe the oscillations of the laser against a near by wall. If they are dead flat then bingo - nailed it - however if the laser wobbles or appears to want to creep away from anything other than a perfectly flat line of oscillation (Flo), we'll rotate the shaft a degree or two one way or the other until I get that flat line. With the shaft in this position we put a bigger line on the top of the tape. This identifies the spine and is the stiffest plane of the shaft that we refer to as S1.
On the left image you can see the flat line we are looking for and on the right you will see how it wobbles:
Now you might be wondering where you should put the soft side (N1) or the stiff side (S1) and that is a good question. Most either put it at 12 o'clock facing the sky or at 9 o'clock facing the target. It is my belief that having the softest axis aligned at the target allows the shaft to kick thru the ball precisely at impact more freely and having the stiffest axis aligned to the sky minimizes the tendency of the toe of the club to droop do to centrifugal force. I have done thousands upon thousands of shafts and it has been my experience that the best performance comes from putting the stiffest axis, the spine, in the 12 o'clock position.
If you'd like to learn more about Spine & Flo you can read Dave Tutleman's article: All About Spines
Until next time,