Universes of Imagination™ - Adventures

This one is simple but one I will use in every campaign going forward. Its pretty common (I even do it as a dm) to send a fireball, for example, to a particular spot because I've measured out the squares that the fireball will hit. I want to do the maximum possible damage with my spell, after all.

But let's think about this for a moment. There I am, in the middle of a battle and its my turn to act (okay, my reflexes and adrenalin have finally kicked in). Am I going to run over to the place I want my explosion to go off with a tape measure AND drag it around for a bit till I have figured out the best spot AND then run back to launch my explosion??????? If I did, I'd be dead already ;-)

So, a simple rule: You can't measure out the area beforehand. You must judge the best position without measuring. Same goes for walls and all other similar effects. If your character has a minute or more to prepare, then you can measure, otherwise not. And if a player chronically seems to be figuring out in his or her head where such things go between turns, then the gm is free to occasionally have the effect misfire!