"Concentration" and "use magic device" skill checks

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How exactly do the "concentration" and "use magic device" skill checks work in IWD2 ?

There's a skill description which is more detailed than in the manual at SP, http://www.sorcerers.net/Games/IWD2/skills.php, but it doesn't answer everything and I doubt everything is correct there.

So how do concentration checks work ?

Do you have to make check when trying to cast close to an enemy ? I never failed a spellcasting because of this, but this doesn't prove anything.

Is the check DC when taking damage depend on the amount of damage taken ?
Is it simply 15 + spell level ?
Or is it 10 + damage taken ?
Or something else ?

I got the impression that the amount of damage dealt does matter but I also remember enemies finishing their spell casting after my half-orc barbarian hit them for more than 100 damage. Is it possible that sometimes the checks aren't made ? My ranger with only 5 concentration could summon a fire elemental (spell level 6, one round casting time) while getting hit by HoF frost salamanders outside Dragon's Eye.


And how do "use magic device" checks work ?
Does it work like described at http://www.d20srd.org/srd/skills/useMagicDevice.htm ?
I had a character with 12 skill try it on level 3 scrolls. She failed far more often than she succeeded. The success chance with level 1 scrolls was about 50 percent.
Is the check DC "20+caster level needed to cast the spell from memory" ?
Has using wands the same DC check as using scrolls ?

 

These descriptions look like there are copied from somewhere, with little relation to the game. d20org, most certainly even farther away. Here is some interesting table.

I would strongly assume thats percentage of success. Try anything with UMD=18

 

I don't know the details either, but RE: your ranger casting while being hit by elementals:

My experience leads me to believe that IWD2 only checks Concentration based on damage once per round. If I'm trying to disrupt a spellcasting, and the first arrow doesn't do it, nothing else will work. It's possible that your ranger just got lucky on the one Concentration check he was required to make.

-Max

 

Concentration checks are definitely affected by damage, as there's nothing more reliable in foiling a round of casting for a horde of enemies than with a single, well timed large caliber AoE damage spell.

So instead of tossing all of your AoE spells into an unsuspecting group of soon-to-become enemies, it's usually advisable that the hardest hitting one hits a second or two later than the rest so that they'll aggro you, start casting and lose it directly afterwards.

 

Rechet, that's a very good suggestion. One AE spell to turn them hostile, followed by the big AE spell to catch the spellcasters in the middle of their first spells. Very interesting idea. You could probably also hold off on any ranged attacks on spellcasters until the first AE spell turned them hostile. They're going to go hostile no matter whether you hit them with everything all at once, or not. So, if you're not confident that "everything" would kill them, then a sequenced attack can gain the value of disrupting their first series of spells. For that matter, you probably don't even need to start the attack sequence with a small AE attack. Even a single ranged attack that would get their attention would probably turn everyone hostile and accomplish the same thing.