This looks like a straightforward linear transformation issue to me (like Fahrenheit to Celsius). Add 50 to all input values, giving you values in the range 0 to 100. Then scale them into your 0 to 12 range by multiplying them by 12/100:
>>> for n in range(-50, 50, 3): ... print n, n + 50, (n + 50) * 12 / 100 ... -50 0 0.0 -47 3 0.36 -44 6 0.72 -41 9 1.08 -38 12 1.44 ... 34 84 10.08 37 87 10.44 40 90 10.8 43 93 11.16 46 96 11.52 49 99 11.88 Did I misread your request in some way? Skip -- https://mail.python.org/mailman/listinfo/python-list