coving problem

hello everyone. I was hoping someone could point me in the right direction. I've had my room plastered and now want to put the coving up. I have got all materials required for the job. I have just started marking my line on the wall and celing. It is 67mm to the edge of my cove. The problem is that if i go 67mm all around the room and mark my straight line it tends to float because i assume the celing is not quite level. Do I go to my 67mm all around or do i just make sure the lines are level right around the room. Its my first attempt and i've prepared properly and just want to do a propper job. Hope someone can help... Cheers

I normally cut a short length of timber, i.e. 67mm, and use it as a spacer scribe. Place one end against the ceiling and your pencil on t'uther and let the spacer trace the ceiling line as you draw with the pencil.

Then do the same for the adjacent angle.

What you end up with is a pair of lines that follow the humps and hollows of the wall/ceiling.

The coving will follow these humps and hollows to a degree but don't go trying to force the coving into tight hollows, just allow the adhesive to thicken up in these spots a bit. This is particularly relevant at corners where two pieces of coving meet as you don't want one piece lower than t'uther, so just go easy when pressing the coving into position at corners.

Why don't you just cut one scribe, Nose and then keep it??!