Here is a quick tip on how to change your signal bars (which could be found in the upper left hand corner of the phone) to numbers (actually decibels). At the end I will explain what the numbers mean.
*No Jailbreak Required!*
Works for iPhone 4, iPhone 4S, and iPhone 5
How to change bars to numbers:
1) Open Phone app
2) Dial the following number exactly (need to enter stars and pounds): *3001#12345#*. Press call
3) You will now be in Field Test mode. In the upper left corner their should be numbers instead of bars. If not tap the bars to enable the numbers. Don't press home or turn off phone yet!
*Continue if you want it to be permanent. If you don't want it to be press home. You can remove it if you continue on, but their is a different way to do that.*
4) Hold down power button (still on the Field Test) until you see 'slide to turn power off' with red arrow.
5) Don't actually slide to turn the power off! Instead, hold down the home button until the Field Test closes and you return home.
6) That's all! Hope it works for you!
The meaning behind the negative numbers: Technically, it is 'the logarithmic unit used to express the ratio between two values of a physical quantity (usually measured in units of power or intensity)'. Basically, it measures the iPhones signal power. All you need to know is the lower the negative number is, the stronger signal strength you have. The higher negative number, the weaker signal strength you have.
