Let say you are closing a dart.
a line from the PIVOT point to where you are closing Dart to. Line_P_D1
a line from the PIVOT point to the nearest point you are moving . Line_P_D2
When you come to roatate the points edit the angle formula to (AngleLine_P_D1 - AngleLine_P_D2)
- may have to fiddle with extra +/- 180 if line is going wrong way.