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 173rd installment in their series of digital spreadsheet magic tricks, you'll learn how to show negative time with the "Use 1904 date system" as well as how to create a formula that will show the time over or under a given hurdle.