What do you mean with "the big and small display"?
On the main user interface the numbers at the bottom displays what you've got it set to and the larger number in the middle of the screen is what the metering circuit in the supply
measures the actual voltage at the output terminals to. Try shorting out the supply, the set voltage stays at whatever while the actual voltage goes to zero, or very close to it.
It's quite annoying that the big displays is higher, makes it a bit useless.
If they were to display the exact same value all the time it would either have to actually BE the same value (ie either the set value OR the actual value) and THEN it would be useless and a waste of screen real estate or the internal circuitry would have to be extremely accurate so that the actual output voltage always matched the set output voltage down to the least significant digit. A 4mV difference between the set value and the readback value is well within its specifications (which is 0.05%+20mV on the set voltage and 0.05%+10mV on the readback).
Oh, and the high resoultion option means you can set the output voltage in 1mV increments (instead of 10mV increments). It doesn't mean that the absolute accuracy of the actual output voltage OR of readback circuitry is increased.
If you still think it's useless, put a piece of electrical tape over it....
Then again, perhaps I completely misunderstodd what you meant by bigger and smaller display in which case you can simply disregard the above.