How to calibrate the DSO Quad

I am having a problem calibrating the voltage on my DSO Quad. I am running APP: 2.45(b)
SYS: 1.41.

I hit the calibrate key and get the “Please connect CH_A input to GND”. Device is connected to gnd and the calibrate key is hit one more time.

At this point device initially says "Input 250-300mv Standard Voltage to CH_A. I connect the channel A probe to a regulated source with voltage 277mV DC. Now, I understand that I need to adjust DIFF column on the CH_A row so that the VOLTAGE reads “+277mV”.

Using Navigator A (-…+), I move the button to the right or left. Neither the DIFF nor the VOLTAGE changes.
If I use Navigator B (ISELECT RANGE <—>) to move to a new voltage, I cannot change the DIFF or VOLTAGE values on that row either.

Any idea what I am doing wrong?

Thanks,

Dick