I have a Weston Master II exposure meter. I got it at a garage sale many years ago and never used it. Recently, out of curiousity I checked it to see how accurate it is. I found that the direct reading in Candela per foot squared is quite accurate but the dial would indicate wrong exposure. For example, 400 c/ft^2 which is EV15 for ISO100 but dial this value in the built in dial I would get 1/130@f/20 which is EV15 and 2/3. Using Weston rated speed of 80 for ISO100 I would get 1/130@f/18 which is EV15 and 1/3. It seems to get the correct exposure setting I would have to set the dial for ISO64 instead.