Where im at the County is divided up into 4 quadrants. Quad 1, Quad 2, Quad 3 and Quad 4. Every department is given a Dept number 1-9 and then members and apparatus have groupings. So Apparatus and Personel have 4 or 5 Digit numbers. Groupsings are as follows, Officers 1-10, FD Personnel 11-50, Ambulances 51-59 Engines 60-69, Trucks 70-75, Utilities 75-79, Support Vehicles (ATV, Command, Wildland, Trailers) 80-89, Tenders 90-95, Water Support (Dive Vehicles, Boats) 95-99, EMS Personel 100-140. So Example an officer for Quad 4 Department 7 would be 4701. Pretty Simple. Always know what the vehicle type or what personel are comming. Based on the quads departments in each quad also have a quad tone in pagers so if a Mutual Aide call goes out in said Quad all pagers in every department in that quad go off regardless of if only 1 department is requested. then everyone knows whats going on too.