Yes, but does the 18" split center? or center
unit? What do you do if a designer wants the other?
Like Ron said, 9" on either side of
unit, or more specifically C clamps 18" apart unless its a double clamp on a mover. Our marks are based off of the Centerline. So Center is our 0 and then on either side we've got 1'6, 3'
etc going off towards the wings. We can accommodate whatever the designers want, we just found that even if a
plot isn't based around 18" our marks are close enough to quickly figure out where their lights will land. It's certainly sped up lighting calls since we've done it.
