A very handy photography rule. In full sunlight,

the correct exposure time for f 16 is equal to the ASA rating of the film

So, if you (wearing your lederhosen) happen to be in Cannes, and you want to shoot a beatiful pictures of Ava Gardner on your trusty Kodak Color Gold 100 ASA, loaded in your Voigtlander, just dial f 16 and choose 1/125s for exposure time.
Why not 1/100s ? Because you don't have it on your exposure time dial. And anyway, that film is not going to notice a 1/4 stop of underexposure.

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