Day 60, Learning 60: GN Mode on Flash

The mysterious and forgotten GN mode... does anybody remember what it's for?  GN  stands for Guide Number, and it's a way to manually set the power of your flash without guessing at the strength.  The Nikon SB700 and above-- and many other flashes, offer this mode.  When attached to your camera, the flash already knows the ISO and aperture settings.  You fill in the approximate distance to the subject and the flash adjusts the strength for the proper exposure.  Why not use TTL mode?  Honestly, that's a fair question nowadays, but GN does have one advantage.  It meters the light in a way similar to a hand-held light meter, which means it's never fooled by color or overall exposure of a scene.