AT&T MERLIN LEGEND Analog Direct-Line Console Operator's Manual page 27

Understanding Your Equipment
DSS Buttons
If your console is a MERLIN II System Display Console, you
have a built-in Direct Station Selector (DSS). Your console's
DSS buttons allow one-touch dialing of co-workers' extensions
to make or transfer calls.
The DSS buttons are assigned numbers in consecutive order,
starting with the button on the top left corner. Each button can
have three numbers assigned to it.
Ask your system manager for the numbers assigned to your
DSS. If your console does not show extension label numbers,
or if you want to change the extensions assigned, see your
system manager.
The following illustration shows an example of MERLIN II
System Display Console DSS buttons. Instructions for using
the DSS and Shift buttons follow the illustration.
1-14 Line and DSS Buttons