Upper and Lower Case Letters (5110/5120 only)
The IBM 5100 was intended more for engineering and scientific work, as a very capable programmable desktop calculator. But the next model, the IBM 5110, was updated to include support for lower case letters (and underline characters). The following note was found on how to activate lower vs upper case mode:
Press HOLD, then SHIFT+UP/DOWN to alternate between upper case and lower case letters.