THE RST SYSTEM OF SIGNAL REPORTING
The RST System of Signal Reporting is used as a shorthand method of reporting Readability, Signal Strength and for CW, Tone (i.e., quality of the CW tone). For voice contacts, only the R and S are used.

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

SIGNAL STRENGTH
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.

Note: The number for signal strength should be derived from the above description and not the receiver's S-meter reading.

TONE
1 - Sixty cycle a.c. or less, very rough and broad.
2 - Very rough a.c., very harsh and broad.
3 - Rough a.c. tone, rectified but not filtered.
4 - Rough note, some trace of filtering.
5 - Filtered rectified a.c.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.

A letter can be appended to the 3 RST numbers if needed:
X = the signal is rock steady like a crystal controlled signal.
C = the signal is chirpy (frequency varies slightly with keying).
K = the signal has key clicks.