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