David H. Ringstrom David H. Ringstrom, CPA, is an author and nationally recognized instructor who teaches over 200 webinars each year. His Excel courses are based on over 30 years of consulting and teaching experience. David’s catchphrase is “Either you work Excel, or it works you,” so he focuses on what he sees users don’t, but should, know about Microsoft Excel. His goal is to empower you to use Excel more effectively. He's currently writing a book titled "Exploring Excel's Hidden Treasures". To learn more about David, you can view his LinkedIn profile and follow him on Facebook or Twitter (@excelwriter).