That's what I'm using, as outlined in detail last year. However,
I never made any claims of relative accuracy because that's not a pissing contest I'm dumb enough to get into (although you're welcome to knock yourself out).
However, I will caution you that if you're going to go after the accuracy of the reading I got, then you will have to explain how my reading matched his on the second video of it doing 2-3sec cuts on some little branch. And while you're at it, maybe you can explain how it runs the same rpm doing 2-3sec cuts on a little branch as it does cutting a chunk of hedge?
Here's the plot of the 2nd (now deleted) video. I got 11,580rpm. The tach was bouncing around so much it was almost unreadable but mostly read between 10,000 and 12,000 rpm:
View attachment 484023
You wanna borrow a shovel?