My new old tool

[Cmark]

This is mine. Picked it up at a Briggs and Scrapiron parts counter many years ago.

 

[JD955SC]

I’ve seen them in the Cat catalog, also seen the analog vibration meters on old rollers.

 

[terex herder]

https://www.ebay.com/itm/194040918642

I had one of them, but I think it got left at a previous employer in a move. You had to have an idea of speed, as it was easy to think you were on speed, but at either a fraction or multiple of actual speed.

 

[pumkinhead]

have had good luck with fuel line pulse tachs on old mechanical cats
https://www.uniquetruck.com/product/13908/diesel-smartach-tachometer?affiliateID=10056

 

[Welder Dave]

There are also tachs that measure HZ like the vibrating wire type but they are a small rectangular box with several indicators going up and down. Found one at McMaster Carr. Also called reed tachometers. Scroll down to the 4th item.

McMaster-Carr