Measurement to breakout

[[Jo...]]

Trying to get an accurate check on a diameter that is the result of a radius and a surface.  It is a large size radius but not much of a length.  I have tried the same methods I have used for a long time.. constraining vectors to get the size and constraining radius to get location.  But I seemed to be way off numbers when plotted in cad software.  sorry for the crude drawing but i cant really share the actual print or tolerances here.  The radius and web is checked VIA a curve for profile of a line so the actual size and location of the radius I do not need, however, the breakout is what i need. I had an engineering request come through on a part that was measured several months ago, so i am re-crunching numbers for them.  When the actual curve points are plotted in cad software, they are showing a different size than what i am getting.  I have a feeling its because of different methods, (ie 3 points in CAD to make a circle vs 500 points "best fit" calypso points) but want to make sure.