In article , kwag98
@usachoice.net says...
I discovered one of these cute little instruments at a hamfest, and I
remember that these were discussed here in RCM before, but I can't find any
posts with google groups search. I've included a proper subject line so that
it can be searched.

This tool is in an original box (and 2 contact tips), but doesn't contain
the instructions. What an odd looking speed indicator.. the input shaft is a
worm that directly turns/drives the numbered dial. There is a spring-disk on
one side with a detent bip that contacts a high spot on the dial at only one
place. This would effectively produce a click for each rotation.

I confess that I really don't know how this tool indicates speed.. and I'm
looking for an explanation from someone wiser than myself


Speed indicator is really a misnomer, revolution counter
would be a better description. It won't indicate speed
without a clock and some math. I've never seen the detent
on the B&S, the Starretts have a bump on the dial that
allows you to count whole revs of the dial as it passes
under your finger.

Ned Simmons