Technical A question for machinists out there

Picked this up yesterday at a garage sale. Seller thought it was for use on a lathe.
Mystery to me. If not for a lathe any ideas what it’s use?

 

Early hand held tachometer.
Used on lathes and machinery.

 

I expect you could see how many revolutions it makes per minute, eh? You'd need your own timer...but this will do the counting for you.

 

you can use to check machine rpm you hold on end of tool and run at say 100 rpm then check gage reading I have a couple just cause I like old tools

 

Found these on ebay.

 

"Set your phaser on stun Mr. Spock"

 

I think its a thingamajigy you lay out in plain sight so everyone asks what it is, and you can sound like a bigshot when you explain all the details

 

I've used one several times. Usually come with several different tips.