What is the meaning of: "You are 5 9 plus 20 dB"?

In amateur radio, the RST system is used to report signal quality. The first number represents Readability on a scale of 1 to 5, and the second represents Strength on a scale of 1 to 9. A readability score of '5' means the signal is perfectly readable with no difficulty. A strength score of '9' indicates an extremely strong signal. Modern transceivers feature S-meters that can measure signals that are even stronger than the maximum standard S9 rating. When a received signal pushes the needle past S9, the extra strength is reported in decibels (dB) above 9. Therefore, '5 9 plus 20 dB' indicates a perfectly readable signal that measures 20 decibels stronger than an S9 baseline.