Quote Originally Posted by Roger Cole View Post
The change from 200 to 400 was due to new standards in the definition, not to any change in the film. Older film speeds were biased to ensure plenty of light reached the film.
Which explains why half the world gets "good results" shooting at half box speed.

Or if you have a working Weston Master II just use it without worrying about the correction.

(Not that I'm saying the word should return to Selenium cell meters. They have their own shortcomings.)