Manipulating throttle output (function)

[DSST\neal.ian]

This isn't a question on how to program or anything, but more of a mathematical question (I put it here because I figured this was more oten visited). My question is this: what is a function/equation I can use to change what the lower bound on the throttle is? I know that it gives outputs from -1 to 1 and to use it I need to negate the value that comes out, since "up" is -1. I figured out a function to manipulate the throttle inputs to get values from 0 to 1, which was (Z+1)/2, of course multiplied times -1 to give the right values. Any thoughts, or questions? Did this make sense at all? Thanks.