HOLLYWOOD STOCK EXCHANGE
THE ENTERTAINMENT MARKET
THE ENTERTAINMENT MARKET
Some reasons
Using what exchange rate?
How do you account for the countries that don't report Box Office to the US or at all?
How do you deal with the Box Office that isn't reported until some days or weeks later?
How do you factor in the different Opening Weekends in different countries?
How do you handle the fact that often different companies have the distribution rights in different countries and/or parts of the world?
By the time you have answers to those I'll have more questions. 
