As a worst-case test, I connected voltages at nearly the full range of the ADC to the DaqBoard. 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. 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.