Hi Brian,
Just to be sure I understand, you have two osc values coming from your tablet. One value is a kind of blackout, so when it is 100%, that means the master intensity should be 0%. Another osc value is a slider (0-100%) that is used when the blackout value isn't active. Is that right?
That would be something like:
if(osc(0), 0, osc(1))
where osc(0) is the blackout value and osc(1) is the slider value. Also, make sure the min&max for your osc values are properly configured in Lightjams in order for the final values to be between 0-100%. Many osc apps send values between 0-1.