Fredy,
Do you mean the range of values inside the CPU?
In this family of PLCs, all the analogues were ranged between 0 and 32000. If you had a signal which had no offset at the bottom end like a 0-10V then 0V=0 and 10V=32000. If you had a signal like yours with a 20% offset at the bottom end, then 0mA=0, 4mA=6400 and 20mA=32000. This also gives you the advantage of doing checks for a faulty transmitter or wire-break. Anything less than 6400 (or say, 4800-5400 if you want to check as far down as 3mA-3.5mA) can be assumed to be faulty. It doesn't matter what resolution of card you're using. All the data was left-shifted in the word, so it was always the Least Significant Bits which were affected, hence the constant range. It made transport of code really easy in this family.
Good luck
Ken