HP 83751A User Manual page 102

The (SHIFT) key causes the secondary function of any key pressed directly
after it to be executed.
When the (SHIFT) key is pressed, the SHIFT annunciator will be visible in
the left-hand display. The next key that is pressed after the @iK) key will
execute the function that is indicated by the blue text that is above the key.
As an example, note that ADDRESS appears in blue text directly above the
secondary function of the (LOCAL) key. Pressing CSHIFT) [LOCAL) will enable
the HP-lE3 address viewing and selecting mode.
the SHIFT annunciator will be canceled from the display and no action will be
taken by the instrument.
without altering sweeper operation.
Instrument State Keys
8-3