I've been using Super Rewards as my micro-transaction system in Dungeon Brawl. They offer a sliding scale coin mechanism with Paypal - the more you buy the greater your discount. What this means is that a coin spent in my game is worth a penny, unless it has been discounted. I have no way of know if a coin has been discounted. Furthermore I am planning on occasionally giving away coins. All of this makes royalty calculations a little complicated because I don't know the value of the coins that were spent on any given game in a month. My plan is to take all income derived for a month and divide that by all coins spent during that month across all of my (expected one day) micro-transaction games to figure out what each title earned in real dollars in that month. I can't figure out a more fair way to do this. Does anybody else have a better scheme?