OK Folks, let's not get too hasty.
The display is NOT inverted.
Your labels are.
I have seen people do this way too many times.
When you prees the top left button, the default should be x21 or x 221 depending on DN length.
It corresponds to the top BOTTOM indicator of the left pair.
When the shift key is pressed and then the top left key, it
corresponds to the TOP indicator of the top left pair.
Here's the way I think of it.
Look at the keyboard on a PC.
The row of keys above the letters are the numbers.
Press a button key alone and you get a number.
Press a button key AND the shift key and you get the character over the number.
Same thing with the M7310.
Press the button alone and you get the lower.
Press the shift and the button and you get the upper.