How to Calibrate the Z depth of the Carrier
Since the distance from the belts to the sliding plate is different on different machines, one should set the depth of the sliding plate drill in the mpc to match their machine. That way, their machine will measure the same board thickness of a board in the carrier as it would if the board was on the belts. I measured the heights of my sliding plates on both my B machines and took the average for the mpc. One has rubber belts and the other has sandpaper and the numbers were quite different.
If you want to make your carrier drill hole accurate for your machine, here is what to do. Place a piece of the 1/2" MDF that you are using to make the carrier in the machine. Clamp it down with the bit touching the MDF. Now turn on the machine. Press 0 - 7 and arrow to the y z sensor data. They will both say 0.000. Move the truck over and touch to the sliding plate. That z number is now what you want to change the drill depth to in the mpc.
(I do not think the drill depth of the brass roller touch point is important for accurate measurement. It just tells the computer about where it will find the sliding plate.)