Mystery tool/gauge

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I did a search for “antique German steam engine mechanical tachometer”. Didn’t find an exact match, but a number of photos of mechanical dial types with the same tip. So I’d say the tool is a steam engine tach.
 

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You had me on the torpedo deal for a minute but my foggy brain remembered I have something similar for my Dad’s machinist stuff. Our friend google shows the exact device below.

High Speed Indicator, a Revolution Counter
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DESCRIPTIONTo count revolutions of the shafts that ran machinery, engineers used counters like this one. The manufacturer, L. S. Starrett Company of Athol , Mass., called the device a speed indicator, although it has no timekeeping apparatus. The steel counter has a flat handle on one side and a rotating cylindrical rod on the other. In between is a flat curved case on which a dial is mounted. Pressing the rod against a rotating shaft rotates it and advances the dial. The edge of the dial is divided into 100 equal parts, which are numbered from 10 to 100 by tens. Two different nozzles fit into the far end of the cylinder. The instrument fits in a red, white, and black paper box. A mark on the dial reads: THE L. S. STARRETT CO. (/) ATHOL, MASS. U.S.A. Another mark there reads: PAT. APR.13.97 (/) MAR.28.05 This counter is one of the many inventions of Laroy Starrett (1836-1922).
Count the revolutions passing 100 within one minute timed in a watch with a second hand and add additional numbers to get the total rpms. Works the same in reverse.
There are Youtube videos showing proper operation.
 
Okay, this has stumped a tool and die maker, a machinest, a machine set-up guy, and a few others...

My grandfather did a lot of woodworking at home,,, built lots of us kids wood toys and puzzles,,, as well as doing lots of other things with tools. Worked on machines at the local paper plants. He had quite the woodshop at home. He passed many years ago, but my uncle lived there until he passed a few months ago,,, so I never really went through the tools until now.
One of the things I found, and probably the only one I have no explanation for is this,,,,
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The little brass numbers in the little circular windows move. The set closest to the pointy tip move when that tip is rotated. The others move with the turning of the little knobs on the side opposite them.

Anyone know what this is, what it's for, how it is used?
Nuclear launch codes found at the president’s think tank??
 
I think some kind of tachometer. The nose of the tool is just like I've seen on other tachs used on lathes and mills. Typically, a machinist has no question of whether the turns counted are left.or right, though, so I wonder if it is indeed used ro check RPM and direction for something like a steam engine or even early electric motor driven stuff. Electric machines accelerated so suddenly that you couldn't easily see their direction of rotation, so maybe it mattered more then to check rotation/polarity as well as number of turns. I wonder if there was a sand timer ( hourglass ) or stopwatch close by this. I use a 15-second sand glass to count turns with my tach in the shop, to adjust the lathe speed for the material being cut. Might be informative to see if twenty turns shows up as " 20 " in the little number windows. If not, then the tool may be converting rpm to feet-per-minute surface speed or other "derived" measure that clues us in on its purpose ( gallons per minute on a pump? Amps/volts on a genrator or megneto?) . Neat instrument. Thanks for sharing.
 
Looks something like manual tachometer I once had. You press the end to the end of a spinning object and it gives a number. I’ll see if I can find mine.
I have one of those manual tachs, and I thought the same thing. If the numbers change with the spinning of the shaft, I would guess it is one of them in a slightly different variant.
 
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