New tool day. I count it as #SlideRule related.
This is an #Aristo 1100 Planimeter, a tool to measure areas from drawings or maps.
The QA sheet inside dates it to about April 1962.
Do I have any clue how it's supposed to work? Nope.
Do I have a manual? Also, nope.
What could possibly go wrong? π€ͺ
Oh. Not to forget: most ends have sharp needles and pointy ends. Totally safe for somebody like me.