Excel 2007 : Rounding Error in Excel calculations

[dav1129]

I have used conditional formatting to show a cell in bold red when it is not equal to zero.

So I could not understand why if:

• The formula for B3 is A3-C3-D3;
• A3=242.57 C3=111.23 and D3=131.34; and
• The result should be 0

Excel displays the result in bold red until I increase the number of decimal places to 14 and discovered Excel was calculating the result as -0.00000000000003

WHY IS THAT?

The same formula does not produce this behaviour for values