Why can't I measure current on my 7700 and 7702 card?

I'm using a 7700 and 7702 switch card in my DAQ6510. I am trying to do switched current measurements on channels 1-10 and can't select current.

Only CH 21 & 22 can switch/measure current directly.
On the other, differential channels, you would need to measure voltage with a series resistor and MATH function to collect a current reading.