Purely speculation on my part it must be some advanced version of :
Total Riders (adjusted for repeat riders)
Divided by:
Total Visitors
Multiplied by:
Total Ticket Sales
Plus:
Merchandise
Possibly some combination of food sales and hotel rooms and parking that they believe are related to the ride
Minus:
Initial build cost
Debt service from initial construction
Cost for upkeep and operation
Other expenses incurred as a result of increased patronage
I think it really depends on how much they compartmentalize and co-mingle their funds.