This belonged to my father, who was a precision toolmaker (mechanical engineer) from the 1950s to the late 1980s
I have no idea what it was for. And sadly I have no more pictures or any other info, and it's not currently local to me.
I originally posted on r/machinists, but the post was removed as they thought I was trying to sell it. For the record, I'm not 🤣
Update: I've asked for the person who has it to let me know if there is any text on it. I'll be back…
Another (non) update: I haven't forgotten. Just don't have a reply yet…