Hi Tony,
I now understand what you are asking. I apologize for my slow grasp of the issue.
Yes, dimensioning the angle will yield extension lines that are perpendicular to the tangent from the endpoints. It will not report the arc length for which I believe you desire.
I suggest that you post this in the customization forum as someone there might already have a routine that does this. In the mean time, you could create an Action Macro that places an arc on top of the circle from the points you designate and then insert a field to capture the arc length.
It is a great idea that might improve the product.
You are welcome to contact the product team directly through the Product Feedback page. The links below go into more detail about the best ways to make suggestions.
How to provide feedback on Autodesk products
Raising enhancement requests for Autodesk products
Another great option is to participate in the AutoCAD Customer Council. This is an opportunity for our customers to partner with the AutoCAD development team to improve future releases of AutoCAD by giving continuous feedback on ideas, designs, and early builds.
In order to get involved email autocad.beta@autodesk.com or autocad.lt.council@autodesk.com
John Vellek
Join the Autodesk Customer Council - Interact with developers, provide feedback on current and future software releases, and beta test the latest software!
Autodesk Knowledge Network | Autodesk Account | Product Feedback