If you are a professional photographer who learned his trade before digital cameras became as widespread as they are today, you probably remember that you had to have your own technique for keeping track of how you took each photo. Most photographers from the non-digital era had to carry around a notebook whenever they planned a photo shoot, and wrote down details such as exposure, shutter speed, aperture, if they used a flash or not, etc. This way, when handling their images in the photo lab, they could tell what they did wrong or what they did right depending on how the photo turned out.