#1
Hey, im tabing a song with natural harmonic i just want to know a bit more about those...

on the E string if you do a 5 NH, that like if you it 24th fret on the same string

(5NH=24)
(7NH=19)
(12NH=0)

That the only one i know, and im not sure all i say is true but is there an logical way to find those?

i speak french...

Thanks
#2
When you divide a string in half, it is one octave higher. If you divide that in half, it is another octave higher. The 12th fret is exactly one half the distance from the nut to the bridge, and the fifth fret is one half the distance from the nut to the 12th fret, so (5NH) is 2 octaves higher than the open string.
#4
If your string were 100 cm. long, the 12th fret would be at exactly 50 cm.
and the 5th fret would be at 25 cm. (and the 7th fret would be at 33.333 cm.)

Your finger resting on the string divides the string into fractional parts of the open string, and each one of these parts vibrates individually
#5
^ Right, and these can also be called intervals, or harmonic intervals. By the way, these interval notes are the reason that some strings seem to want to start vibrating all by themselves even though you've not strummed or even touched them. And it's why a 12 string sounds so nice. It's all in the octaves.