Weird Excel Calculations

[Allen]

Has anyone ever noticed Excel calculating things weirdly? Like when you try and total a list of numbers that do equal zero but it comes up with an exotic number that's really close to zero?

Try the following. All the figures below add up to zero yet I keep getting the same result.

2484.33
191.8
-2484.33
-175.8
-16

Whether you add the up in the same cell or enter them into difference cells and =SUM them together it brings back the result 1.70530256582424E-13.

I know this is something crazy like 0.0000000000000170530256582424 but why can't it do a simple calculation like this correctly??

[smashie]

have a look here, it's a well known problem with floating point arithmetic