AASTRA 4225 Vision for MX-ONE (TSE) User Guide EN - Manual (Page 101)

101 Dialog 4223 Professional/Dialog 4225 Vision
Settings
Dialog 4225 Vision:
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Select PhoneSet in the top menu (see display).
Down or Up Press to frame
Set Hearing Level
(see display).
Select Press (see display).
A tone signal is heard, and the display shows the current setting. The
Line 1 key lamp also indicates the current setting;
key lamp off=standard level, key lamp on=increased level.
Change Press to change the volume level (see display).
The display shows the new setting. The Line 1 key lamp also indicates
the new setting as described above.
Exit Press to finish setting (see display).
When extra amplification has been selected, the Line 1 key lamp turns
off.