I also collect various vintage drafting tools like old technical pens, and lettering sets. I thought it may be fun to make this post to see what else you guys collect.
This was a very recent eBay purchase- I have to admit that prior to seeing this I had no idea it existed.
This is the ACU-ARC ruler by Hoyle Engineering. The instructions say it can be used to draw an arc of any radius from 6.75 to 200 inches. It came with a case, instructions and warranty card dated 1972.
