AT&T System 25 - Manual (Page 20)

Coverage
If your System Administrator has administered this feature, calls
to you can be answered (covered) at specified telephones when
you do not answer the call yourself. Calls unanswered at your
telephone will start ringing at the covering telephone after a
preset number of rings. However, if you are busy on another
line, calls will go to coverage after a preset number of rings
(usually one).
Buttons used for Coverage answering are:
Coverage calls for one specific person are sent
to an Individual Coverage button assigned to the extension.
Coverage calls for a group of two or more
extensions come in on a Group Coverage button associated
with the group the extensions are assigned to.
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