Step 7 - Encoder

Hi I am trying to control the position of an encoder using step 7.

I want the position to change when the set point demands it so if position 1 is 10 and position 2 is -10 this would activate a change? I tried using a comparator block but if the tird position is -20 this activates a change again so the motor drives forward when it should be in reverse.

Any help would be greatly appreciated.