m. instantaneous/time switch
When set on ”I” the camera will give a consistent exposure to all single frame exposures when the run switch is moved to the “P” setting. When set on “T” the shutter will remain open for as long as the run switch is held on “P.” This only effects single frame shooting. It is a good idea to keep this switch set to “I” most of the time so that if you do single frame shooting and haven’t checked it, then chances are it will be set correctly.
“I” stands for instantaneous and “T” for Time exposure.