Comment 1 for bug 1329945

The forma to calculate the signal strength depends on the technology, and our ofono-rilmodem driver basically converts the ASU values to percentage (0-31, 99).

Here's how android calculates the signal bars (for GSM):
"""
   int asu = getGsmSignalStrength();
   if (asu <= 2 || asu == 99) level = SIGNAL_STRENGTH_NONE_OR_UNKNOWN;
   else if (asu >= 12) level = SIGNAL_STRENGTH_GREAT;
   else if (asu >= 8) level = SIGNAL_STRENGTH_GOOD;
   else if (asu >= 5) level = SIGNAL_STRENGTH_MODERATE;
   else level = SIGNAL_STRENGTH_POOR;
   if (DBG) log("getGsmLevel=" + level);
   return level;
"""

So in order to have a similar result, here's the range and bars based on the output from ofono (0-100%):
>= 38% - GREAT (4 bars)
25% <= x < 38% - GOOD (3 bars)
16% <= x < 25% - MODERATE (2 bars)
6% <= x < 16% - POOR (1 bar)
0% <= 6% - NONE or UNKNOWN