Day 248/24. Does anyone know what this is?

A strange object donated to the museum as a part of a draftsmans briefcase. This was amongst various drawing tools. We have no idea what this thing is? It's about the size of a pen.
The flat handle can be rotated to show numbers. The further out the numbers are wound, the more the spring loaded metal head (with a ball on the end) can be depressed.
The markings on it say Chartoak - Made in USA
We have no idea what it is, or what it is used for. Any ideas?