memberhsip function range in fuzzy logic

i have problem with the membership function range i am working with fuzzy controller for boost converter my set point is 40 and the error changing from -40 to 40 but most of the papers put the range from -1 t0 1 i donot know how ?any one help me with this please ?

as the output also range by logic the duty ratio cannot be negative but they put the range the same with error and change of error

the attatched files from previous published papers for the system i use