What does the guard rune in Quake-Live do exactly?

It has been suggested to use the Guard rune to combat people using rail and the Doubler rune. What does it do exactly?

For now I'll reference this holysh1t article, citing damage taken being halved. I suppose there's more to it than that, especially regarding armor (which seems more effective with the rune.)

I and that good brony of a Tristan have done a little bit of science, and it turns out holysh1t got it wrong. That's just how much people at the highest levels care about maps with runes. Anyway!

Getting hit with 100/100 (= 100 hitpoints, 100 armor) by a direct grenade hit:

YOU              THEM  Without doubler      With doubler
Without guard             66/34 (-100)       49/1 (-150)
With guard                83/34 ( -83)       75/1 (-124)

Getting hit with 200/0 by a direct grenade hit:

YOU              THEM  Without doubler      With doubler
Without guard            100/0  (-100)       50/0 (-150)
With guard               150/0  ( -50)      125/0 ( -75)

We also tried with one hit from a plasma gun (20/30 damage) and the results are consistent with the above.

Guard halves damage taken by your hitpoints after your armor absorbed damage normally.

From what I recall, armor soaks two damage points every three. Now, with guard every second hitpoint damage is skipped.

This means that:

• You get one sixth less damage (-17%) so long as you have armor to absorb damage.
• You get half damage (-50%) when you do not have armor.

Considered that doubler appears to be a flat +50% damage boost, this means guard actually has the edge over doubler, although in this match up the guard player's armor will evaporate real fast.

(Oh, another thing. Scout does not make you get more damage than normal.)