Les makes a good point. For your question there are two ways to adjust an analog signal. One is with gain and the other is with offset
Gain is a multiply/divide process. 1, 2, 3, 4 with a gain of 2 produces 2, 4, 6, 8. 1, 2, 3, 4 with a gain of 0.5 produces 0.5, 1, 1.5, 2.
Offset is an addition/subtraction process. 1, 2, 3, 4 with an offset of 2 produces 3, 4, 5, 6. 1, 2, 3, 4 with an offset of -0.5 produces 0.5, 1.5, 2.5, 3.5.
Which of these is what you are trying to achieve?
ak