Depending on the cellular standard used, different criteria for rating the actual reception conditions apply. The scale of the signal indicator reaches from 0 (no signal - red) up to maximum 4 (very good reception - green).
The current Signal is indicated in a scale from 0 to 31, where a high value indicates a better signal; 99 stands for no antenna connected. This value is just a rough guide value that represents the received level only.
RSSI (Received Signal Strength Indicator) is the original value of the signal field strength in dBm. This value is only significant in a 2G network; therefore, it will only be displayed if the modem is registered in a 2G network.
RSCP (Received Signal Code Power) in dBm and Ec/No (received energy per chip divided by the power density in the band) in dB are only significant, if the modem is registered in a 3G network. The inferior of both values is decisive for the signal indicator.
RSRP (Reference Signal Received Power) in dBm and RSRQ (Reference Signal Received Quality) in dB are only significant, if the modem is registered in a 4G network. The inferior of both values is decisive for the signal indicator.