I'm a professional maritime photographer in San Francisco. And I've been shooting for years. I understand the difference between different metering patterns (spot, center-weighted averaging, and pattern). And I know, too, the kinds of lighting and subjects that are likely to fool a camera's meter, and have learned to compensate when dealing with those. I almost always shoot in aperture priority, and dial in exposure compensation to compensate as needed. For instance, I'll bump exposure up 1 or even 1 1/3 stops when shooting wide shots under gray skies, preferring to keep the clouds bright, and bring up the detail in my darker subjects. Or if a boat sails in front of a dark background, I'll compensate -1/3 or -2/3 to keep the dark areas dark, and hold detail in the white sails. Recently some of the exposures calculated by my 5D MkII have me wondering what I'm missing. I don't understand what is causing exposure to be so far off in some scenes. I will attach some samples below.