Keysight Technologies N778 C Series Programming Manual page 17

Introduction to Programming 1
The SESEM allows you to choose the event that may affect the ESB of the
Status Byte. If you set a bit of the SESEM to zero, the corresponding event
cannot affect the ESB. The default is for all the bits of the SESEM to be set
to 0.
Unused bits in any of the registers change to 0 when you read them.
NOTE
Keysight N778xC Series Polarization Instruments Programming Guide 17