New to Microsoft Excel? Looking for a tip? How about a tip so mind-blowingly useful as to qualify as a magic trick? You're in luck. In this MS Excel tutorial from ExcelIsFun, the 183rd installment in their series of digital spreadsheet magic tricks, you'll learn how to sum revenue from a table of data by year and month using the SUMPRODUCT, TEXT, SUM, IF & LEFT functions in an array formula.