Netting off to zero
 

Hi,

I have a spreadsheet in Excel that has 129 entries, each of which I have
copied and pasted from another document.

When I do a sum of these (which should net off to zero), the total is:

0.000000000294676283374429000000

However, I then went back and set the "Number Format" for all of the 129
entries to show the same number of decimal palces, and to my surprise I found
that after the first two decimal places (which were effectively "pence" and
cantained non-zero digits), the remaining decimal places were all zeros.

Can someone explain why excel is displaying the sum as non-zero (for info I
calculated the 129 entries manually using a calculator and it does indeed
equal zero). Is this something to do with the fact that computers cannot
accurately represent decimals as they using binary code as opposed to our,
human, base 10 code?

Many Thanks,

Gary T.