Quote Originally Posted by R.K View Post
So in most of the situations you don't nead an average value. Am I right?
If you have a spot meter with a Zone scale on it, and you expose/process using some semblance of the Zone System, then, no, you don't need to average. Simply place subject luminance values where you want them, adjust development as needed (assuming B&W film), and you're golden. You don't even need a spot meter, if you can accurately measure middle gray with whatever meter you have; read middle gray and do the mental calculations from there. Heck, you don't need any meter! Brett Weston never used one.