Exposure compensation is a technique for adjusting the exposure indicated by a photographic exposure meter, in consideration of factors that may cause the indicated exposure to result in a less-than-optimal image. Factors considered may include unusual lighting distribution, variations within a camera system, filters, non-standard processing, or intended underexposure or overexposure. Cinematographers may also apply exposure compensation for changes in shutter angle or film speed (as exposure index), among other factors. Many digital cameras have a display setting and possibly a physical dial whereby the photographer can set the camera to either over or under expose the subject by up to three f-stops (f-numbers) in 1/3 stop intervals. Each number on the scale (1,2,3) represents one f-stop, decreasing the exposure by one f-stop will halve the amount of light reaching the sensor. The dots in between the numbers represent 1/3 of an f-stop. Exposure compensation on still cameras In photography, some cameras include exposure compensation as a feature to allow the user to adjust the automatically calculated exposure. Compensation can be either positive (additional exposure) or negative (reduced exposure), and is frequently available in third- or half-step, less commonly in full steps or even quarter-step increments, usually up to two or three steps in either direction; a few film and some digital cameras allow a greater range of up to four, five or even six steps in both directions. Camera exposure compensation is commonly stated in terms of EV units; 1 EV is equal to one exposure step (or stop), corresponding to a doubling of exposure. Exposure can be adjusted by changing either the lens aperture or the exposure time; which one is changed usually depends on the camera's exposure mode. If the mode is aperture priority, exposure compensation changes the exposure time; if the mode is shutter priority, the aperture is changed. If a flash is being used, some cameras will adjust flash output as well. Adjustment for lighting distribution The earliest reflected-light exposure meters were wide-angle, averaging types, measuring the average scene luminance. Exposure meter calibration was chosen to result in the “best” exposures for typical outdoor scenes; when measuring a single scene element (such as the side of a building in open shade), the indicated exposure is in the approximate middle of the film or electronic sensor's exposure range. When measuring a scene with atypical distribution of light and dark elements, or a single element that is