[yiforiyo]

Let's s suppose that my character , a technomancer get an 0,2 essence cost augment , how much resonance he would lose ?

Resonance 6
Essence 6

[Xenon]

The intent (for this edition) seem to be that you can spend almost 1 point of essence on augmentations before both your maximum resonance and your current resonance drop by 1 point.

[MercilessMing]

Your Current Resonance drops 1 immediately, your max resonance doesn't go down until you get to 5 essence.

Pg 38, Essence:
(specifically, anytime your Essence goes below any whole integer, you lose a corresponding point of Magic or Resonance).

Pg 168, Initiation:
Your maximum Magic rank is 6 + Initiate Grade (reduced by one for every full point of Essence lost).

Pg 195, Increased Maximum Resonance:
The natural maximum for your Resonance attribute is 6 + your Submersion grade (reduced by one for every full point of Essence lost).

[Xenon]

I'd say this is likely a result of bad editing. That the original author's intention actually was to explain that your current Magic is reduced by 1 for every full point (every whole integer worth) of Essence lost.

The alternative (that at 5.9 your current magic is reduced but you are allowed to spend karma to raise it back up and later, at 5.0 your maximum magic is reduced by 1 and then your current magic is reduced again at 4.9 essence) is pretty strange, not at all streamlined and [obviously] not intended (if you ask me).

[MercilessMing]

I'd like that better too.  Definitely more streamlined, and adds some tolerance for magic and tech mixing, which this game needs a little more of.  But since this wording has survived 3 errata, I think the awkward way is the actual RAW.