Atan[3]/[20] works in Mach3 Gcode, not in an external card. If you have Mach3 on a PC with no connection to a controller or machine then you can use:
G90
#50=Atan[3]/[20]
g0 A#50
and the DRO for the 4th axis will show the correct angle.
If I then use G68 A0 B0 R#50 you can see the Local System has changed to +8.5
This is on my laptop that I use for work away from my workshop. As I said though, you need to have the 4th axis enabled.
