Yamaha O2R Owner's Manual page 159

UNDO Operation
When the 02R stores or recalls a program, the previous settings are always
preserved in the UNDO buffer. If you discover you have made a mistake,
you can always recall the UNDO buffer (displayed as "U:" in the scrolling
list of programs). Use the CURSOR buttons to select the RECALL icon, then
rotate the encoder wheel until the UNDO buffer is the current program,
and press the [ENTER] button. The previous settings are restored.
Program Name
Equalizer program names can be up to 16 characters long and can contain
any of the following characters:
MIXING Display Functions
Digital Recording Console 02R User's Guide
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