The Mandelbrot set is mathematically generated sea of numbers which together constitute a fractal. Wikipedia says much better informed stuff about it than I do in their article on the subject.

This spreadsheet is my attempt to generate a representation of the Mandelbrot set inside Excel. The set is generated without any macros. It requires Excel 2007 because it uses colour scale conditional formatting to represent the output, and it needs more columns than Excel 2003 had. It's unable to take advantage of the multi-threaded calculation engine in Excel 2007, because it has circular references and it's unfortunately impossible in those circumstances for Excel to know how best to farm out the calculation tree. There are no VBA functions in the sheet, but it does need iteration switched on - make sure you open it in a fresh session of Excel to ensure that the calculation settings are right.

• Version with no macros (but slightly harder to zoom)
• Version with macros (and zoom buttons)

If you think you can improve upon the sheet then please do get in touch - I'm not claiming it as a great paragon of spreadsheet excellence.

Chris Rae, 30 May 07 (updated 10 Nov 09)