Okay been quite curious for a while about what this buff actually did, now when my EE finally reached lv 58 I thought about finally make a real test of this one, and so I did.
How we did this test was basicly calculate how much more P.def you have between the buff and with the buff. We also discovered a few other things :)
Anyway for the data of this test: http://lineage2.mugimugi.org/shield.htm
Now first we tried to hit a naked dwarf without anything but a shield, the top data is that. No block is the damage taken without a shield block., second line is the damage with a shield block, and last with advanced block.
The formula we calculated out the P.def on the shield is (damage no shield/damage with shield)*P.def = Your current P.def. The first test we got out 396 P.def more or less and subtracted the chars normal P.def we ended up with 247... Okay this is an interesting number, as the shield we tested only have 230 P.def. Our conclusion was that the Shield buff also affect the shield aka add an extra 15% P.def to it, sure the numbers here is a tiny bit off, we only used 10 hits as our source, going to do a better one later on.
In any event then we tested it with Advanced Bloc 1k, result here ended up that the shield have 401 P.def now, In other words aprox 60% more P.def.
The second test on the page is with another armor, Plated Leather to be exact, same thing applies there more or less, same shield to.
So, our conclusion is that Advanced block 1 add 60-65% P.def on your shield, also that the Shield buffs also add it's 15% to it. In other words lets say it's 60% exactly. That means if your char got both Shield 3 and Advanced block your doom shield will have 426 P.def instead of the 230.
BTW the formula for calculate P.def now that I got it as on a shield block with Advanced Block 1 is this.
(P.def + (Shield * 1.6)) * 1.15
So E.G a user with 700 P.def and a doom shield with 230 P.def buffed with those things have basicly an P.def of 1228 P.def :)
No shield block it would be 805 P.def
And lets say you average shield block at a rate of 60%, it means that you have an P.def of 805+(426*0,6) = 1060 P.def
I still can't wait to see what Advanced Block 2 will add, but for now I'm very happy of what Advanced Block 1 adds, quite a lot of P.def in the end. Hope this was somewhat useful as well.
PS I know my English suck, but I'm not an native English speaker after all.