Nokia 252 - Manual (Page 10)

6
Signal Strength Indication
A cellular phone sends and receives radio signals. As with all
radio equipment, the quality of radio reception depends on the
strength of the radio signal in the area where you are operating
your phone.
The strength of the cellular signal is shown by the
vertical bar on the left-hand side of the display.
The higher the bar, the stronger the signal at your
present location.
When NO SERVICE is displayed, the phone is either
outside of the cellular service area or restricted from
entering service, and calls cannot be made or
received.
If the signal is poor and you are using the phone in a building,
you may get better reception near a window.