THE RST SYSTEM

Readability

1–Unreadable
2–Barely readable, occasional words distinguishable.
3–Readable with considerable difficulty.
4–Readable with practically no difficulty.
5–Perfectly readable.

Strength (Signal strength can be read from the S meter when receiving.)

1–Faint signals, barely perceptible.
2–Very weak signals.
3–Weak signals.
4–Fair signals.
5–Fairly good signals.
6–Good signals.
7–Moderately strong signals.
8–Strong signals.
9–Extremely strong signals.

Tone

1–Sixty cycle ac or less, very rough and broad.
2–Very rough ac, very harsh and broad.
3–Rough ac tone, rectified but not filtered.
4–Rough note, some trace of filtering.
5–Filtered rectified ac but strongly ripple-modulated.
6–Filtered tone, definite trace of ripple modulation.
7–Near pure tone, trace of ripple modulation.
8–Near perfect tone, slight trace of modulation.
9–Perfect tone, no trace of ripple or modulation of any kind.

Signal reports are exchanged when Amateur Radio operators contact each other.
For Morse code (CW) communications, all three are used. A very good signal report would be 599.
For voice communications, only readability and strength are used. A very good signal report would be 59.