G4 Dwell parameters

[M250cnc]

well there are two answers:
a) I want to implement a gcode interpreter "properly" so I need to know what the G4 syntax means
b) I am using Eagle to lay out PCBs; the gcode converter spits out a (G4 P3) delay after starting the spindle
clearly that needs to be 3 seconds not 3 mSeconds!

make sense?

Yes, so you need to configure the control so that P3 is 3 seconds and not 3 milli seconds.

Phil