I think You should know what a Group Master is, first.
It seemes to me, that You think, that a Group Master (GM) will affect the Output will change the Date in the Cues. That is not what it is for.
The GroupMaster is like a Grand Master and is reducing (or increasing) the (Dim-)Levels of a group of Lamps regardless of what the Lamps are getting from the Programmer or the Cues.
So if YOu have Dimmer in the Cue (or Executor-Fader) set to full, then the lamp will only be fully turned on, when the desired Group Master is at Full to. Otherwise the GM will reduce the Output of the Dimmer Channel.
I hope I explained that right... Otherwise maybe you take a look in the manual...
But as I am writing here: I have a Problem with GMs.
I have a "chinese Lamp" which is similar to the Clay-Paky B.Eye (ETEC - Mini-Eye 7 (with only 7 RGBW Lenses instead of 19 or more)) and I don't know what I have could done wrong - but my Group Master won't work with them. They have a real Dimmer and I want to store different Dimmer Acttions (e.g. Sound to Light, Fades, Tapped Chasers,..) with the inbuilt Dimmer and want a Second "over-all-Dimmer" who will reduce the Brightness regardless of what is programmed in my cues (or in the programmer). So I declared one Executer Fader as the GM of my B.Eyes, but it does absolutely nothing. The Lamps are always "full on" if I programm them or giving them a signal from a Cue.
And I've checked the Programmer window and the DMX Table as well.
Should I choose another kind of Master or might there be a big issue in my Headfile?
How can it come up, that a GM won't have any effect on my Output?