Spell Skills Clarification

[askari]

Hi, I'm sorta new to GURPS, and I just signed up to this forum(waits for the round of "Hi, Askari"'s to end)
My question deals with spells. I understand that each spell is a separate skill, but I'm having...issues with determining exactly what to roll against. Supposing I have an IQ 13 character with Magery, oh...1, and I have three ranks(guess who also plays D&D?) in Purify Air, what do I roll against? 17, the total of IQ + Magery + Spell? Or do I roll against 4, the total of Magery + Spell? Or 16, the total of IQ + Spell?
I ask this because I'm getting conflicting answers from the book. It speaks of base skill and effective skill and I'm getting muddled about it, and at one point - though I may have merely been tired and misread it - I could have sworn that the book made mention of success rolls being made against only the skill ranks...
...so obviously I'm certain you can all appreciate that I'm either stunned or stupid and require clarification.
That also leads to another question: allowing for my above example with Purify Air at 17, would that allow the 1 FP reduction detailed on page 237 of the Basic Set - Characters?

[Mathulhu]

IQ 13 and Magery 1 just add when using spells

Skill 3 ranks, does this mean you've put four points in it to get an IQ Hard skill equal to IQ

Spells work just like skills, your relative level the X in IQ+X, only matters when you are using the skill in a special/innovative way.

So we have, four points gives Spell = IQ + Magery, in this case, = 14

So you roll under 14 to succeed.

[askari]

Forgot about the Easy-VH thing...but yes, by 3 ranks I meant 4 points to buy a Hard(-2) skill, thereby getting IQ 13 + Purify Air 1 = 14. So to cast Purify Air I'd have to roll against 15, to account for Magery 1, correct?

[Dinadon]

Right, base skill is just the skill level written down on your character sheet. Effective skill is what you roll against after taking into account modifiers for a particular check. If there are no modifiers, then effective skill = base skill.

Remeber that buying skills in GURPS means buying it at a level relative to its controlling attribute. The table at the start of the skills section tells you how many points you need to spend get a given difficulty skill to a particular level relative to the attribute. In most cases the skill's level is the sum of the attribute level and the relative modifier, so if you buy a skill at attribute+1, and you had the attribute at 11 then the skill level would be 12.

For Magery (and Talents) you need to do one more step before writting it down on your character sheet. So let's say the previous example was a spell. If you had Magery 2, you would then add it's level to the skill's level, giving you 14. This is then the skill's final level, and is what is written down on your character sheet. (If you wanted the reductions you get at a spell level of 15 you can either improve the attribute (IQ), the skill, or Magery by a level).

When making the roll, you'll be taking the value of the spell as written on your sheet, and then rolling equal to or less than that on a roll of 3D6.

[Mathulhu]

Where did the Purify Air 1 bonus come from?

Purify Air is the skill in question, the 4 points were spent on making it equal to IQ, then you add Magery for a total of 14.

[askari]

@Dinadon: Thank you very much, that was exactly what I needed to know.
@Mathulhu: The Purify Air 1 was simplified. IQ 13 + Purify Air (3 - Hard 2) + Magery 1 = 15. Purify Air is a Hard skill, which means it has a -2 modifier. Very Hard has the -3 modifier.

[Mathulhu]

IQ Hard Skill
1 point IQ-2
2 points IQ -1
4 points IQ-0

[askari]

Remember when I said I was either stunned or stupid? I know which one it is, now.