In the 'good old days', when we had finished the day's photography, we would disappear into the darkroom and spend hours breathing in the fumes of nasty, smelly chemicals in the pursuit of our art, now we have Adobe Photoshop.
More and more consumer digital cameras are now including a histogram display either during the Record mode or in the Playback mode. This tutorial explains just what the histogram is and how you can use it to ensure a correctly exposed picture.