This is on page 21 of the user manual. It appears to address what you are asking.
1. CAL Signal
The “CAL Signal” provides access to an internal amplitude calibrator signal of 80MHz. Pressing the Î key toggles the reference signal between “Off” and “On”.
2. Option Report
The “Opt Report” provides access to the current configuration of the GSP810 including optional hardware that is installed. Pressing the Î key displays a screen showing Software Version (SW), Firmware Configuration (FW), Tracking Generator Configuration (TG, where “N” means option not installed), Receiver (R), Power Meter (PM) and Reference Signal (REF). The “TG”, "R" and "PM" labels will be followed by “N” if the option is not installed. The “REF” label is followed by two fields that identify the status of a 10 MHz system frequency reference signal that can be applied to the unit. The first field will display “STD” for standard and “IMP” for improved. The second field will display “INT” for internal 10MHz reference, or “EXT” for external 10MHz reference.