Computers Do Make Mistakes !

Spreadsheet calculations are also subject to the limits of accuracy imposed by the way they operate.

Study the example below carefully

Why aren't the cells B4 and B6 equal, surely 27.05 - 26.1 = .95 ?

Is this caused by a Fault in Excel ? or perhaps the Pentium bug ?

In fact its neither. Its cause lies in the fact while we operate in the decimal system, computers operate in the binary system of 1's and 0's.

The computer converts between the two systems. However it turns out that some decimal fractions do not convert neatly to binary numbers.

The problem is similiar to that of converting 1/3 to an exact decimal equivalent.

1/3= .3333333333333 where do we stop with the threes ?

The computer too is limited in the amount of space it can use to represent numbers so it is sometimes forced truncate them.
This means the binary equivalent of some decimal fractions is close but not exactly correct.

That's the reason for the error above.

Try formatting Cell B4 to 15 decimal places to see if you can see the problem.

In spreadsheets (in fact in all computing) errors of this nature while small can become significant when multiplied thousands or millions of times.

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