I believe I have found an excel bug.

To replicate it put the following simple formulae in excel.

In A1 put: 2.7
In A2 put: -4.3
In A3 put: 2.2
In A4 put: =5.2+(-5.8)

In A6 put: =sum(A1:A4)

If you make A6 show as many decimal places as possible you will suddenly
discover a very small number is being produced. Oddly if you set A4 to
contain -0.6 then it solves the problem.

Any ideas what's going on?

Alex.