Technical Drawing…. Stuff?

Having come over all enthusiastic regarding creating mandalas yesterday (I shall post one at some point) I thought I’d have a bash at home. However, a pair of compasses is necessary. I remembered that my Dad (who at one time was a Draughtsman) used to have some.
I didn’t find what I was seeking but this interesting box came to light.
I wonder how the instruments work?!

I have been on a four hour Zoom training course today, so drawing isn’t on my agenda tonight. I hope suicide isn’t either, which was the subject (as in ‘prevention of’, as opposed to, ‘how to’).