[Superman]

I draw in Alphacam- it is very similar to Autocad - It just has a machine / cam function built in to the software. I can dimension radius, diameter, horizontal, vertical and aligned geometries. But cant seem to find a way to dimension circumference.

You may not be able to dimension an arc, but surely you can analyse an entity and get its length

There is not much of a requirement to have a circumference dim on a drawing, but as a circle dia X pi is an easy calc. to place into a notation.
A bit harder for a part circle, but you should have a way to analyse features.