Another rule (connected somehow with f/16) is the following:
Northern side of clear blue sky 45 degrees above horizon at noon is middle-grey.
I use it occasionally to check, when in doubt if my exposure meter is sti= ll accurate, but more often as a reference point, when shooting objects whic= h are far from middle grey, for ex&le snowscapes in bright, sunny days - = just point your camera at sky, AE-lock exposure, compose, and shoot.
My own modification of the above is this: although with this procedure yo= u obtain middle gray objects middle gray on your slides, but sunlit snow, w= hich is more than 3 f-stops brighter than middle-grey, is washed-out. To make = it look nicer, I underexpose the sky by 1 f-stop. This makes the sky really = deep blue and middle grey objects (trees, people, etc.) underexposed, but when= the main subject of your picture is snowy landscape, it looks ok. So my own r= ule for shooting snowscapes is:
Dial -1 f-stop exposure compensation, point the camera at sky (not necess= arily at north, but away from the Sun, horizon and clouds), AE-lock exposure, compose, and shoot.
For me works, esp. in the mountains, so well, that I stopped bracketing, = since I'm pretty sure my slides are exposed just as I want them to be. I wish I= had a spot meter in my camera, since when the sky is partly clouded and I use= a wide angle, it becomes tricky to get rid of clouds when metering...