Why is a cell reading as 0.80000001 when it should be 0.8?

[Academic_Data]

I have a formula that is doing a simple subtraction between two cells. The result of this is being used in a Index(Match) function, but I am sometimes pulling an error because the cell seems to be reading as 0.800000000000001 instead of 0.8. The subtraction in question is just essentially 10.8 - 10. I checked that there are no hidden decimals in the 10.8 and the 10, and there are not.

Any ideas why this is occurring and what I can do to fix this?

 

[BobUmlas]

Computers work in binary, not decimal, so it's as close to .8 as it can get using subtraction in binary.
You can get around this by using the ROUND function, something like =ROUND(A1-A2,3)

 

[Aladin Akyurek]

I have a formula that is doing a simple subtraction between two cells. The result of this is being used in a Index(Match) function, but I am sometimes pulling an error because the cell seems to be reading as 0.800000000000001 instead of 0.8. The subtraction in question is just essentially 10.8 - 10. I checked that there are no hidden decimals in the 10.8 and the 10, and there are not.

Any ideas why this is occurring and what I can do to fix this?

Look up on floating point maths, etc.

In the meantime use, something like:

MATCH(TRUNC(A1*10)/10,MatchRange,MatchType)