Using a dial to update another dial's variable

I have two dials. Dial1 turns from 0-90, and Dial2 turns from 90-0. I have set the variable of Dial2 to that of Dial1 so both dials turn when you turn Dial1.  I am trying (unsuccessfully) to automatically decrement the value of the Dial2's variable when the Dial1 turns. What I want to happen is when Dial1 variable increments from 0-90, Dial2 decrements from 90-0. I know I can use multiple triggers to do this, but is there a way to do this without having to create 90 triggers? Any help is appreciated. Thanks!