Spells with +1/x levels

[Jimp]

I'm a tad confused with calculating bonuses and such on spells with +1/x levels.
1. For spells like Divine Favour that read +1/3 levels (minimum +1) do I take it that at 3rd level the bonus would be +2 or still +1?
2. For spells like Spiritual Weapon that read +1/3 levels [Note that no minumum is given] do I assume that I have +0 until 3rd level when I get +1?
Also, for all of these:
3. Is it +1/class level or effective caster level?
4. For +1/3 levels is it for every 3 levels in total or for every 3 levels AFTER you gain access to the spell level?

Thanks.

[Fax Celestis]

1. It'll be +1 until level 6.

2. Yes.

3. Caster level.

4. Caster levels in total.

[FujinAkari]

I always played that +1/3 levels would become +2 at 4th level, as the description seems to imply you round up, but I could (easily) be wrong

[Lord Lorac Silvanos]

Math suggests that you don't and D&D rules agree.
You never round up unless it specifically says so. (In D&D, not math)

[henebry]

Spiritual Weapon is a 2nd level spell. So you don't get access to it until you're third level. This means the minimum + to damage is +1, unless you have some means of casting the spell before attaining third level.

I should add that the SRD entry for Spiritual Weapon helpfully specifies "dealing 1d8 force damage per hit, +1 point per three caster levels (maximum +5 at 15th level)." So Lord S is right.