Field test using iOS 12

I just got an iPhone XR and I have iOS 12.1 on T-Mobile. The field test mode works fine with this setup. Just dial *3001#12345#* and select “LTE” and then select “Serving Cell Meas”. On the next screen, look for “rsrp0”, which is the received power level in dB from your primary cell tower. “rsrp1” is the signal power level received from the next best cell tower. The received power level should have a value from -50 to -130. The lower this numbe, the better your cell reception will be. A power level lower than -110 starts to be problematic. A level below -120 is dead zone territory.