Making an iPhone show a numeric network signal strength

I am enjoying my vacation on the east coast of Spain at the moment and noticed regular bad quality/dropped calls and a varying reception on my cell phone from place to place. In order to look for the strongest signal I have enabled displaying the signal strenght in db (Decibel) on my iPhone 4 using the instructions from this Lifehacker article:

To enter Field service mode and enable displaying the signal strength in db on your iPhone perform the following steps:

  1. Dial the number *3001#12345#* and press Call
    The iPhone will now enter Field Test mode, the  signal strength indicator in the upper left corner is now displaying a numeric signal strength in db. One can toggle between signal strength bars and numeric db value by taping on it.

    To make this feature permanent, complete the next two steps (simply press the home button to abort and exit the Field Test mode)

  2. Press and hold down the power button until the ‘slide to power off’ screen appears (but do not power off the device)
  3. Press and hold down the home button until this screen closes and the home screen appears

The signal strength can now be toggled between bars and numberic db value, the closer the numeric db value is to zero, the stronger the signal is. Toggling between signal bars and numeric db value persists after a restart of the iPhone, but the process is completely reversible. To return to the default behavior and have the bars permanently, follow the following steps:

  1. Dial the number *3001#12345#* and press Call
  2. Press the home button to exit the Field Test mode.

 And your phone will behave as before, no more numeric db signal strength when you tap the left upper corner.

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