Caster Level and Dual Class

Hello,

Does anyone know how caster level interacts with dual class? Do spells that check caster level only check the level you were in the class that allowed you to cast the spell? Or is it the highest level you have in any class?

For example I was thinking a Priest of Helm 3 to Fighter Dual might be cool. You would have Seeking Sword and Draw Upon Holy Might for free sort of, but would be a lot better if they didn't last for 3 rounds or only give +1 to the stats respectively.

I'm on iPad so I don't know if there's a way for me to use the console that is often mentioned to test this stuff out myself easily?

Thanks!