What does "RST 459" mean in a Morse code contact?

As with all Morse code signal reports, the RST system evaluates Readability (R), Strength (S), and Tone (T). The Readability scale maxes out at 5, while Strength and Tone max out at 9. For a report of "RST 459", the "4" indicates the signal is quite readable, meaning it can be understood with practically no difficulty. The "5" on the 1-to-9 strength scale means the signal has fair strength. Finally, the "9" represents a perfect, pure tone. Other options are incorrect because they mistake the middle-of-the-road "5" strength for either very strong (which would be an S9) or very weak (which would be an S1 or S2).