Isn't this all a bit academic anyway?
The tolerance (or allowable error) from a VOR is +/- 4 degrees
The tolerance (or allowable error) on a OBS is +/- 1 degree
If you were 60nm from the VOR and 1 radial (degree) off track and both the VOR and your kit were exactly correct that equates to 1nm lateral displacement which, whilst IFR would be iffy*, VFR would let you see what you were supposedly "over"
* Which is why it would never be used for an IFR approach
Are you measuring your angle to the ARP or a runway?
What is the problem you are trying to solve?