A good reference book. It does require some knowledge of statistics for the more advanced functions described.
On another, somewhat related, note.... I really hope that all of the steps described here work on a Mac. If you are a serious Excel user I highly recommend sticking with a PC computer. Many of the more advanced functions don't work with the Mac version of Excel or come out years later and the menus are laid out differently so Excel tutorials based on Excel for PCs require the extra step of figuring out how to do things on a Mac. Unfortunately my office is a Mac office, otherwise I'd switch to a PC in a heartbeat.