switel TAF 80 Mode D'emploi page 58

Starting Up
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If you ever want to change the basic settings, start Programming mode by pressing
the button  for 4 seconds. Use the selection buttons y and z to
navigate in the menu. Press the c button to select the respective menu option.
If the battery becomes fully discharged, the basic settings must be entered again.
To delete a digit from the local access or international dialling code, use the
selection button y or z set a minus sign (−).
Press the C button to exit from the menu at any time.
If there is no input for a period of 30 seconds, programming is automatically
cancelled.
Press the u/CHECK button to check the day and time announcement.