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1PO, 2PO. 3PO, 4PO - POlarity
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Set to one of the following:

    0 = Normal motor polarity
    1 = Invert motor polarity

Polarity sets which direction the motor will turn when presented with positive and
negative Gcode coordinates. It's affected by how you wired the motors and by mechanical
factors. Set polarity so the indicated axis travels in the correct orientation for your
machine.

Travel in X and Y is dependent on the conventions for your particular machine and CAD 
setup. Typically X is left/right movement, and Y is towards and away from you, but 
people often set up the machine to agree with the visualization their CAD program 
provides, and can depend on where you stand when operating the machine. Typically X+ 
moves to the right, X- to the left, Y+ away from you, and Y- towards you. Z is by 
convention the cutting axis, which is the vertical axis on a typical milling machine. 
Z+ should move up, and Z- should move down, into the work.

 3PO = 0        Set polarity to normal
