"ambulance tours" is an indication of the amount of units on the road. FDNY or hospital based 911 ambulances work, AFAIK, 8 or 12 hour tours. So a unit that is scheduled for 3 8 hour tours, that is actually in service for those tours, would be credited for 3 per day, or at total of 1095 per year.

I know it sounds weird, but when I worked in EMS they treated the different tours like they were entirely separate units. Performance metrics were measured and reported per individual tour.