Both good suggestions, but too time consuming. I've been shooting in rooms recently with a ton of window light. I also use strobes at the same time. So, when clouds roll in, the light changes drastically in the room and shooting manual just isn't working. I use my 1ds Mk3, set on AV, and let the camera's computer keep my exposures consistent. I don't want to put my clients through the inconsistency of any other method.