Why do I have this?

[Ultradog MN]

Doing a deep clean inside my pickup and found this under the seat.
Dunno where it came from or how it got there.
In a box of odd junk from an auction?
I know it's a tachometer.
What do you do - use a stop watch and time it? I like it but it'll probably go into that drawer of odd tools that doesn't get opened very often.

 

[Mike(NEOhio)]

Speed indicator is kind of a misnomer. It actually counts revolutions and you must time it. Common in machine shops.

 

[Charles in Aus.]

I have a ' Starrett ' branded one , quite useful for determining the number of rpm a vintage un instrumented tractor's pto shaft is running at .

 

[greenmech]

Doing a deep clean inside my pickup and found this under the seat.
Dunno where it came from or how it got there.
In a box of odd junk from an auction?
I know it's a tachometer.
What do you do - use a stop watch and time it? I like it but it'll probably go into that drawer of odd tools that doesn't get opened very often.

I have one too, may have used it once! Ron MN

 

[T.R.K.]

Daddy had one. Its still around here someplace. He used it in the Cotton mill to check the speed of some of the machinery. That was before digital everything. Your wristwatch (with hands, not numbers) must have a second hand, and while your wristwatch counts off a minute by the second hand going around its' face, you must also simultaneously count the times the little dot goes around. Then you multiply the number of times the dot went around by the ratio of the gears inside to get the rpm of the machine. As I recall it had a flat rubber pad and also a pointed rubber pad that interchanged on it.

 

[T.R.K.]

"Not numbers": well actually, there were numbers from 1 to 12 arranged in a circle. Just not digital numbers.
Nowadays, there is probably an 'app' for your telephone that can do the same thing.

 

[leroy in ne]

Bump on moving dial is so you can feel each dial revolution allowing you to watch second hand. 1 dial revolution is 100 shaft revolutions