DBM signal strength instead of bars

I read about this somewhere and thought it was useful. I am not a big fan of the (number of bars) method of reporting signal strength. They are so generalized as to be not vary useful. So I went hunting and found a note about getting signal strength in DBM instead. There is a field test app hidden on the phone and it will change your signal report to DBM. I went looking for this info mainly because I was testing a cell repeater kit for improving coverage inside a building. Making the change to DBM over bars helped. Anything better than minus 75 seems to be great. I can make calls at minus 95 but much lower than that and it is hit or miss. So here is how to set it. From your phone dial *3001#12345#* That is (star, digits 3 0 0 1 pound sign digits 1 2 3 4 5 pound star). Then hit the call button and you are in field test mode.Now touching the signal strength with a double tap will switch back and forth between DBM and bars. If you want to make this change part of your normal operations then do this. Press and hold screen lock until you get the slide to turn off message. Don't do that. Instead hold the home button until you have your home screen back. Now your signal strength is in DBM. Single finger double tap the signal strength to switch back and forth between DBM and bars. If you just want to check it out then you exit the mode with the home button instead of using the screen lock method. Note that some web sites say this mode was not available on all versions of IOS.