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, without any macros. It requires Excel 2007 because it uses the new 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 present 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.

In case you don't have Excel 2007 (or you really can't be bothered opening the thing) here's a screen shot.

There's no nice way to zoom in and out of the set - you'll have to manually edit the numbers in the top right. 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