There have been several threads in the past where people lamented that their Domino would not center a mortise accurately using the plastic indicator scale. Sometimes there isn't enough room to slide the scale far enough to the side to correct the problem. I encountered this on my new Domino and also noticed that when I centered a piece in the cross stop the two scales didn't read the same left as right. They differed by 1.5 mm! After studying this a while, I believe I have found the cause, a fix, and an easy way to check and adjust the centering 
The problem on my unit was that the tilting fence was not centered with respect to the rest of the machine. I could measure different distances from the center line on the bottom of the base to the two sides of the fence.
You can test this alignment by making an accurately square piece of wood and then scribing a sharp line around all four sides perpendicular to the edge. Put the tilting fence at 90 degrees and put the test piece of wood against it and the base of the Domino, pushing the two locater pins in so that the wood is tight against both the tilting fence and the base. Align the scribe line with the center line on the base of the Domino. It can be helpful at this point to clamp the wood to the fence with a couple of spring clamps. Now turn the unit over and look at the top of the tilting fence. If the scribe line on your wood does not fall exactly in the center of the triangular cutout in the fence, your fence is misaligned! Likewise, the center line on the plastic scale should be exactly aligned with the scribe line.
If your Domino is misaligned, start by recentering the tilting fence. It pivots on two pins in the fixed base, and they are held into the base by 2mm set screws from the bottom. Loosen these set screws and push the tilting base whichever way is necessary to make the triangle cutout fall exactly on your scribe line. Then retighten the set screws. Now loosen the two T10 screws that hold down the plastic scale and put its center line exactly on the scribe line.
The acid test, of course, is to do the alignment test described in the excellent supplementary guide available in the Gallery. Mine was now dead on, and the cross stop scales now match when a piece is centered!
The problem on my unit was that the tilting fence was not centered with respect to the rest of the machine. I could measure different distances from the center line on the bottom of the base to the two sides of the fence.
You can test this alignment by making an accurately square piece of wood and then scribing a sharp line around all four sides perpendicular to the edge. Put the tilting fence at 90 degrees and put the test piece of wood against it and the base of the Domino, pushing the two locater pins in so that the wood is tight against both the tilting fence and the base. Align the scribe line with the center line on the base of the Domino. It can be helpful at this point to clamp the wood to the fence with a couple of spring clamps. Now turn the unit over and look at the top of the tilting fence. If the scribe line on your wood does not fall exactly in the center of the triangular cutout in the fence, your fence is misaligned! Likewise, the center line on the plastic scale should be exactly aligned with the scribe line.
If your Domino is misaligned, start by recentering the tilting fence. It pivots on two pins in the fixed base, and they are held into the base by 2mm set screws from the bottom. Loosen these set screws and push the tilting base whichever way is necessary to make the triangle cutout fall exactly on your scribe line. Then retighten the set screws. Now loosen the two T10 screws that hold down the plastic scale and put its center line exactly on the scribe line.
The acid test, of course, is to do the alignment test described in the excellent supplementary guide available in the Gallery. Mine was now dead on, and the cross stop scales now match when a piece is centered!
