One of our club members brought this in to show n tell at our last meeting.
Anyone have one or know how it works?
It might be off of a Hoyt Clagwell.
Please forgive me.
Could be for a small flywheel magneto engine, like lawn mower. The case seems 1950's ish.
That would explain the ranges, idle and then hi-speed, as those little gas engines are run at full.
eBay listing with a manual of Hoyt testers, including the 634.
Thanks for that link, yep, says for single cylinder flywheel mag engines.