A refractomometer for measuring Brix
This is total web research (nothing I knew) but apparently the guy who made it is emmanuel goldberg. I found that on a site about compasses.
Looks like one of those things the mechanics in the Army used to check out batteries and coolant. They would put a little drop on it and then look into the light.
Asked one of them once what the heck that was and they called it a Duo-Check. Anyway found one on ebay link. Yes I know I am likely wrong, just saying it looks like one of them things.
https://www.ebay.com/p/Reichert-Duo-chek-7181-Coolant-and-Battery-Tester/1420390306
That's also a type of refractometer![]()