Figure 2 shows the results. There's about a 30-mV difference between the values measured with the DMM and those measured with the DaqBoard. Recall that when I used a single channel, the voltage differences between the DaqBoard and the DMM were a few millivolts. The 30 mV of error might not matter in your application, but it's enough to throw the DaqBoard out of spec. Still, this type of error is common among multiplexed ADC boards.
Noise reduces an ADC's useful bits.
I next looked at the DAQBoard's noise to get an idea of how many bits I would really get to use. Figure 3 shows the ADC noise. Ignoring the extremes as random errors, which could have been caused by EMI from the PC, I found that the DaqBoard loses at least three bits of resolution to noise. Through DaqView's acquisition setup page, I set the DaqBoard's internal clock speed to 200 kHz. I used the function generator to generate an external TTL-level clock signal, but the DaqBoard's driver indicated an error when the clock frequency reached 100 kHz.