Using slider to have only one correct position?

Hello! I'm trying to use a slider to change the state of a human in a training exercise where only one position on the human (and thereby the slider also) to be correct. 

I'm trying to hide the "next" button and make it show up only if you have the slider on say step 8 of 10. I've tried with the triggers that already exist, but the button just tries to either stay hidden or not hide at all, even if you're at step 8 on the slider or not.

The slider is rigged to 10 different states of an object that changes state every time you move the slider.

I'm making this as a school project and I'm very interested in this program. It would be nice to make this thing work!