Michael Alexander is a Microsoft Excel MVP who has written several books on advanced business analysis with Microsoft Access and Excel. Visit Michael at DataPigTechnologies.com for free Excel and Access training.

John Walkenbach, arguably the foremost authority on Excel, has written hundreds of articles and created the award-winning Power Utility Pak. His 50-plus books include Excel 2010 Formulas, Excel 2010 Power Programming with VBA, and the bestselling Excel Bible, all published by Wiley. Visit his popular Spreadsheet Page at spreadsheetpage.com.