IIRC the Mark III is a Rawson in a different dress. I have a Rawson hooked to a 2600 and zero for a rate is a no no. If you are spreading fert you could try 10 as a min. I don't think it will cause it to turn the drag. It's a pain but I learned the hard way this spring. The console will not accept a zero commanded rate. You can turn the dial on the Mark 3 down to find the lowest non-zero rate. That will have to be your minimum-then when you get to that area of the field just turn the switch OFF. If you are spreading lime you will have to have a higher min. The only way to know is to enter the midpoint in the console and manually turn the rate knob down to find the lowest non-zero rate or calculate it according to step size. The rx minimum must be over half of the calculated controller minimum as that will cause it to go to the closest step. Clear as mud? Email is good.