What is this Starrett piece?

[ConductorChris]

Have this Starrett piece. Don't know what it's called or what it is for. Would appreciate any info you guys might have.

 

[Dumber than lumber]

You might want to ask Starrett.
But it looks like an indexing or dividing device. Pictures aren’t that great.

 

[Mintgrun]

It is a tachometer, or "speed indicator".

 

[WisJim]

It's a speed indicator. Hold the tip against the end of a rotating shaft for a measured time, read the total revolutions off the dial, and calculate the RPMs. Google "speed indicator" and you will probably get lots of info.

 

[d42jeep]

I found these at an estate sale in October. A Starrett and a Craftsman, both with their boxes.
-Don

 

[Roberts210]

I've used them, they can be pretty accurate, if you can time accurately.

 

[RTM]

Here and following.

https://archive.org/details/StarrettToolsCatalogNo25/page/n253/mode/2up

 

[Cleave]

I got one of those for almost nothing at a farm sale. Like yours, mine came without the wheel. So it will measure rpm if you can put it into a center hole in the shaft. But with the wheel you can measure surface feet per minute. So I turned a wheel like Tubalcain did for the video below. It will be fun to use with our boys when they're old enough to learn gear math, then we can compare theoretical vs. actual rotational velocities and surface feet per minute, working the gear math in between.