Nikon D3300 Reference Manual page 320

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The Nikon Creative Lighting System (CLS)
Nikon's advanced Creative Lighting System (CLS) offers improved
communication between the camera and compatible flash units for
improved flash photography. Refer to the documentation provided
with the flash unit for details.
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Guide Number
To calculate the range of the flash at full power, divide the Guide
Number by the aperture. If, for example, the flash unit has a Guide
Number of 34 m or 111 ft (ISO 100, 20 °C/68 °F); its range at an aperture
of f/5.6 is 34÷5.6 or about 6.1 meters (or in feet, 111÷5.6=approximately
19 ft 10 in.). For each twofold increase in ISO sensitivity, multiply the
Guide Number by the square root of two (approximately 1.4).
300 Technical Notes