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.

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.     

If the signal has the characteristic steadiness of crystal
control, add the letter X to the RST report. If there is a
chirp, the letter C may be added to so indicate. Similarly
for a click, add K. The above reporting system is used on
both cw and voice, leaving out the "tone" report on voice.

The above report codes recommended by the A.R.R.L.