What do all the numbers on the film box mean?

[Jeff G.]

The wife "master of chemistry who must be obeyed" is out of town, and I am loading film tonight, and wonder what all the numbers on the film box mean--I see the ISO number then there is a slash and another number with a degree sign after it ---one box I have is 14 and one is a 17 --these are different films, but I just have no idea what that other number is with the degree sign---

[Mike Kovacs]

ISO is the melding of the American ASA and European DIN standard. Hence it shows both standards.

[Luca Merlo]

The DIN number is the measure of the light sensitivity of the film according to the German Standard unit in logaritmic scale. The ASA is the same figure according to the American Standard in artimetic scale. My suggestion is to use the American figure since it is much simpler to use (the doublig of the figure is the equivalent of 1 stop difference).

[Leonard Evens]

"ISO is much easier to use"

I think it is a matter of taste and what you are used to. One DIN unit corresponds to 1/3 stop. Three DIN units corresponds to one full stop. Since my lenses are marked in 1/3 stops, it is pretty easy to make adjustments in aperture. If you do that first, then changing the speed/aperture combination is easy.