My collecting is Antique Technical / Engineering Drawing Instruments.
It relates to the frustration I had wanting to become an Architect in my youth and failing. My son is a very successful Architect but typically shows no interest in my collections of around 40 boxed sets as in the photos below.

A general View of some boxes and individual pieces.

More Boxes.

An Individual Box and a Proportional Divider

My Oldest Piece - a Brass Ink Pen
I have collected quite a few Ink Pens separately. I just love the Hand Made (Mostly in Holbourn London a hundred years ago.