Wich variable to Override ?

I try to override left position with script but when I use variable in return value nothing happen.

If I use a number it is OK. (Return 50)

What variable format I need to use ?

var rpm = value;
 double rpm2 = Convert.ToInt32(rpm);
 
 rpm2 = rpm2 / 40 + 74;
return rpm2

Is bad, I try to convert rpm2 to string, int, double ...

Ok, I think in my different test I miss something, it is working with:

var rpm = value;
		 int rpm2 = Convert.ToInt32(rpm);
		rpm2 = rpm2 / 40 + 74;
		return rpm2;