The strength of a flash unit is often indicated by a guide number. Similar to camera stops, flashes have special stops as well. They are known as flash ability, and are assessed in fractional increments. They are also often described as, full power, half-power, quarter-power, etc. Moving one-step at a time along this size (from full capacity to half-power or from half-power to quarter-power) is one stop difference.
Precisely the same change as when modifying your shutter rate or aperture one stop. Based on your unique display model or brand, 1 /2 or even 1/3 stop flash power increments might be possible, similar to in-between shutter speed and aperture modifications. On some flashes, the power is displayed as a direct conversion on the display LCD screen.
