When I first started using colour film (transparency) in 1959, accurate exposure became critical, and guessing or using guide like the one shown on the left in the photo was inadequate. As the Agfa Silette had no built-in meter, I used the moderately priced meter shown on the right of the photo above. The meter has a rolling blind which covers the meter cell when you want to use incident light metering, and also a guide in the side to assess colour temperature. The meter is still working, though the maker’s name badge fell off at some stage.