If I think through things I can be pretty accurate outdoors during the day. For me the problems seem to come up when I am inside, or at night. I know that if I shoot something in my kitchen in the evening, lit only by fluorescent, I typically shoot black and white for EV 7, a little different for color because I typically use daylight film and a fluorescent filter.. I know this from experience. But if I am at someone elses house in the evening I am not certain that is correct. And my eye is not good enough to meter the light. So using a meter is the only way for me to really know.