This greatly enlarged 3rd edition continues to exploit the convenience and transparency of the spreadsheet while enhancing its precision and accuracy. It teaches through detailed, fully worked-out examples, many taken from the literature, with extensive comments. This third edition contains*** New visualization tools, added emphasis on common computational pitfalls, and many new examples, plus an extensive set of directly applicable sample functions and macros for often-encountered data analysis problems, all open-access and freely available under the GNU General Public License.*** A collection of 125 additional matrix functions (increased from Excel"s 5) including for eigenvalue and singular value problems of real and complex matrices, thanks to the work of Leonardo Volpi and coworkers.*** About 300 additional functions for calculating in extended precision, of up to over 32,000 decimals, covering all of Excel"s Math & Trig, Statistical, and Engineering functions and many more, a project started by Leonardo Volpi and recently greatly enlarged by John Beyers. *** Still, you can use just as much power as you need. The included least squares macro xnLS operates as easily as its double-precision cousin LS, and only needs 35 decimals to ace all of the NIST StRD linear regression tests, decimal for decimal.*** All of these free, open-access add-ins retain the ease of use and transparency of the spreadsheet, and do not require you to write any VBA code. If you ever doubted the computational power and accuracy of Excel for scientific data analysis, read this book, try out its exercises, and judge for yourself. *** However, if you want to create VBA routines to solve your own problems, or wish to write special functions for your students or coworkers, extensive help is provided on how to write and validate these, and to make such custom add-ins fit seamlessly within Excel.