I found something very interesting there: "They place the card next to the subject and meter from it. This is equivalent to incident light metering: measuring the light that reaches the subject. With incident metering, the exposure is independent of the subject's reflectance: dark subjects come out dark and light subjects come out light. Incident metering works very well in studio environments and for close-ups, but it isn't practical for landscapes. Meters built into cameras measure reflected light." ;) I guess that's why my yesterday pics were so god damn dark!!!