The deluxe marking wheel holder has a knuckle joint so that the cutting wheel can be adjusted independent of the scriber.
It does the same job as the marking wheel holder but has more versality allowing the angle of the cutting wheel to be easily changed without having to move the body of the scriber.
Scoring a line on the work piece gives a definite datum point and as long as you cut accurately to that scored line your fit will be better than cutting to a pencil line.