What does the left pitot tube supplly air pressure to?
Pilot's side ASI, Air Data Computer and airspeed/mach warning switch
What does the right side pitot tube supply air pressure to?
FO's ASI, Air Data Computer, Airspeed/Mach switch and also.....
The gear horn!
What does an "OFF" flag on the altimeter mean?
The ADC that drives the altimeter is not reliable.
It also means anything else the ADC drives is not reliable.