Modern management practices developed before the US civil war

In Angry Birds, you can use in-app purchases to improve your experience. A “King Sling” upgrades your slingshot for “maximum power and velocity”. A “Birdquake” will bring the pigs’ defenses “crashing to the ground” When a gamer buys power ups, how does Rovio Entertainment (the publisher of Angry Birds) account for items purchased not yet used? The intensification of slavery in North America posed similar questions to financial managers.