The USS version has an RS-485 interface to the CPU. The analogue one has an ADC interface to the CPU. Both interfaces use the same pins on the front panel, so you can't have both.
There should be a model number on it somewhere - in the form: 0AB2a-bxy0* a = 1 2 or 3, b = 0 1 2 or 5, x is U or A, and y is A or B. * is anything.
The interesting ones are x and y - For x, U is unfiltered, A is filtered. For y, A is Analogue, B is USS.