You've heard of Sweet 16, but probably not sunny 16 unless you are a photographer. Maybe not even then. I've been taken photos for several years and thought I knew about exposure. But the Understanding Exposure course I am now taking has shown me that I barely knew the basic. And I did not know about Sunny 16.
On a sunny day, an aperture setting of f/16 will correctly expose a sunny subject if the shutter speed is one over the ISO. For example, if the ISO is set to 100, then setting the shutter speed to 1/100 sec will result in a correct exposure. No need to look at the light meter. If the ISO is set to 200, then setting the shutter speed to 1/200 is the correct exposure. Again this works with the aperture is set to f/16. The sunny parts will look terrific and the shady parts will be black.