Measuring the signal strength at the receiving antenna is one way to determine the quality of a communication link. If a distant transmitter is moved closer to a receiver, the strength of the transmitted signal at the receiving antenna increases. Likewise, if a transmitter is moved farther away, signal strength at the receiving antenna decreases.
The RSSI is measured in dBm. A greater negative value (in dBm) indicates a weaker signal. Therefore, -50 dBm is better than -60 dBm.