The Leica DB R4 databack replaces the standard camera back door, and provides the option to manually expose the date, time, and the letters A to K into the bottom right-hand corner of the picture together with the exposure.
Modes:
Day selector
Numbers from 1 to 31 and one empty field
Month selector
Numbers 1 to 12, letters A to G and 2 empty fields
Year selector
Numbers 80 to 99, letters A to K and 2 empty fields
On/off switch
Selector for the adjustment to different film speeds
Cable connection to the flash contact of the camera
Battery test button