Most modern SLR film of digital cameras with a built in light meter have an ISO dial which allows the sensitivity to be set.

For digital this allows the sensitivity of the CCD to be set for a specific situation and it can be altered for every shot. For instance in a low light situation the ISO might be set at 1600 where as for fine work the ISO might be set at 100.

However, with film the ISO relates to the preset sensitivity of the emulsion and the ISO is set for all the shots taken on the roll of film.