A player's effective caster level for purposes of using a scroll is equal to his character level. The player may not use a scroll with this skill if the scroll requires a higher caster level than the player's character level.
Artificers have an effective caster level of two higher than their class level, or their character level, whichever is greater, when determining whether or not they can use a scroll. However, when using a scroll, the Artificer uses his actual Artificer level to determine at what level the scroll's spell functions. This may result in a spell that would be otherwise weaker than the minimum possible.
A player using a scroll with Use Magic Device may activate the scroll at any level between the scroll's minimum level and his own character level. Attempting to activate the scroll at a higher level results in a commensurate increase in the Use Magic Device DC.