True Sceadwian, but this is used in clubmaking, I guess you would call it a static measurement as opposed to dynamic.
These machines are manufactured and sold. I built another clubmaking tool and a part of that tool was the vise assembly, it turned out really well, when I got through I realized I have halfway to having a golfclub frequency meter, the vise being a major component (and not as simple a task to achieve as it may seem). The part I was lacking was a sensing unit (infrared emitter and sensor) and the processing part (to count the breaks and convert that number to cycles per minute) and the display (an led readout). There was an existing plan on the internet for one, a home project type, but upon closer inspection most of the parts were obsolete and hard to find, it used EPROM.
https://www.tutelman.com/golf/measure/fmeter.php?ref=
However on another board there was a reference to using a pc to be an fm, via the soundcard and soundcard software.
**broken link removed**
A friend of mine familiar with the application suggested using a microcontroller, but that would require in his estimate 50 to 100 hours of programming.
I could purchase the completed unit of the pieces I need for about $180.
https://csfa.com/default.htm
However, funding for play toys is at an all time low right now and the $50 range was much in my budget.
I did find an EPROM at an arcade part dealer, and in his description he offers to program it for an additional $3, he asks for an image, I do have some downloaded files from the original plan (DaveT's), I not sure if thats what he would need or not. Outside of that, there are several other obsolete parts from the plan and I not sure how other substitutions would fit.
Thats about where I am on it right now, its taken several hours of researching and thinking to even be able to discuss it this clearly, if I am even being clear.
I have zero electrical background, other than don't touch the two wires together, but I like to think that I have the average intellect, but as of this point I'm beginning to wonder. Hence my offer to barter for assistance.
Now Sceadwian I could discuss the dynamics of the golf swing with much more intelligence than I do electronics.