HP 54710A User's Reference Manual page 109

Channel Menu
Calibrate
Best Accuracy Calibration Memory The oscilloscope displays either
protected or unprotected. Protected means that the mainframe memory
is write protected so you cannot perform a best accuracy calibration on
the plug-in. If you try to perform a best accuracy calibration when the
memory is protected, the message "Best Accuracy Calibration Memory
Protected" is displayed at the top of the screen. Then, you must set the
best accuracy calibration switch on the rear panel to unprotected before
continuing with the calibration.
The best accuracy calibration switch on the rear panel is normally left in the
unprotected position. This allows you to perform a best accuracy calibration
at any time without having to change the switch setting.
Plug-in This lists the model number, serial number, date, time, and
temperature delta. The temperature ∆ is the temperature change from
the temperature of the mainframe when the last best accuracy
calibration was performed. If this temperature ∆ is more than ±5 °C from
the last mainframe calibration, then you must perform a best accuracy
calibration to achieve the one percent accuracy specifications.
6–14