Exposure and shooting
DX code
A coding system on 35 mm film cartridges and film edges that lets cameras and processing machines identify the film.
The checkerboard of metal and insulated squares on a 135 cartridge tells a compatible camera the film’s speed and length. A barcode printed along the film edge identifies the film for processing equipment. Cameras without DX reading, and film without a code, rely on the speed being set by hand.