Sum show difference of -0.000000000002501104298755

[Chuck]

The spreadsheet was created from an Access query where the column is defined
as double with 2 decimil places.
In Excel I expand the column to 30 decimal places and none of the values
have anything but 0 past the second decimal place.
Yet when I =SUM(E1:E763) I get the total of -0.000000000002501104298755.
I have tried changing the format in Excel to currency, general, accounting,
no change?
Any ideas would be appreciated.

 

[Sheeloo]

See http://www.cpearson.com/excel/rounding.htm for an excellent article on
the subject...

 

[Harald Staff]

Yet when I =SUM(E1:E763) I get the total of -0.000000000002501104298755.

You are the dictator of 250 000 people. Each one of them (happily) pay you
this amount of dollars every minute, day and night, all year through.

After X time you can buy a hot dog with your tax money.

X is ?

Question / problem is ?

Best wishes Harald

 

[Chuck]

Thank You Sheeloo. I read the article but am not sure it applies to this issue.
When I expand the decimal places on the column to 30, there are only 0's
after the second decimal place for each cell in the sum. But the sum has
values other than 0 starting in decimal position 13 thru 24, then all 0s to
position 30. I would thing there would need to be some value besides 0 in
position 25 thru 30?

 

[Fred Smith]

Chip's explanation applies, Chuck. You're adding in decimal, but computers
add in binary. Conversions from decimal to binary are imperfect, especially
in decimal positions 13 to 24. If you want the sum to be exactly zero, you
need to round your numbers.

Regards,
Fred.

 

[dlw]

in 10 years you'll have $3.29 (rounded, of course)
unless my Excel is wrong... :>)

 

[joeu2004]

I read the article but am not sure it applies to this issue.

Well, it does. But I can see how its relevance might be lost in its
overwhelming detail. Try this pointer: http://support.microsoft.com/kb/214118
.. I think the first paragraph directly addresses your problem.

When I expand the decimal places on the column to 30,
[....] I would thing there would need to be some value
besides 0 in position 25 thru 30?

Well, there are. But Excel formats only the first 15 "significant
digits" (i.e. not including leading zeros). I don't know exactly what
your value is; but as an example, if I enter the 24-digit decimal
fraction that you posted into an Excel cell, the exact internal
representation is exactly
-0.00000000000250110429875499,985154767000935027774881358464398317664745263755321502685546875.
(Note: I use the comma to denote 15 significant digits to the left.)

The bottom line is: even for simple financial computations, it is
prudent to make liberal use of the ROUND function. That will not
eliminate the numerical "error" that is inherent in the representation
of most decimal fractions in the standard binary computer format. But
it will probably be sufficient for your purposes.

Alternatively, you might use the Precision As Displayed calculation
option. But I do not think that is a good approach.


----- original posting -----

 

[Chip Pearson]

Often, programs do not test for perfect equality due to the
limitations of floating point representations. Instead, a difference
less than some very small value is considered equal. E.g.,

Const MIN_NUM As Double = 0.00000000000001
Dim A As Double
Dim B As Double

' A = some calculation
' B = some other calculation

If A = B Then
' might have floating point problems
End If
' instead use
If Abs(A - B) < MIN_NUM Then
' close enough to be considered equal
End If

Some languages (e.g, C/C++) have the MIN_NUM value defined as part of
the standard package for just this sort of thing.

Cordially,
Chip Pearson
Microsoft MVP
Excel Product Group
Pearson Software Consulting, LLC
www.cpearson.com
(email on web site)

 

[Chuck]

Wow, and who said computer guys were geeks, this could be auditions for the
comedy channel.
FYI, the query in Access that creates the spreadsheet has Round(x,2) for the
column.
Then I tried =Round(E2,2) on the spreadsheet for all the rows and still get
the hot dog in 3 years, which of course I'll share with my 250,000 subjects.