The combination of aperture, ISO and shutter speed is called an exposure value (EV). Any combination of settings irrespective of value, that gives the same exposure, has the same EV. Exposure value is also used to indicate the interval on the photographic exposure scale, more commonly known as stops. A stop is the doubling or halving of light that is hitting the sensor by changing one of the three elements of the exposure triangle. A change in ISO from 100 to 200 is an increase of one stop as the sensor is more sensitive to light. A change of Shutter Speed from 1/125 to 1/250 is a decrease of one stop as the shutter speed is faster and light doesn’t have as long to hit the sensor.