(Borrowed from the firmware update notes in my 990 review...) Pressing "SELECT" and "INPUT" on the front panel at the same time while the unit is in standby displays the version number, but be careful because "SELECT" and "MENU" will reset the unit to factory defaults. The version number is displayed as "Version x.xx xx" with the first set of numbers ("x.xx") representing the firmware version (3.10 for the May 21 release, for example) and the second set of numbers (" xx") reflecting the build date of the particular 990 being updated.