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Simple Forumula is returning 3.63797880709171E-12

Posted on 2006-06-01
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Last Modified: 2006-11-18
Hi

I am trying to write a qry that does a simple minus calculation.  To explain I have created two other qry's that sum two tables. These two qry's are called

qryTotalPayments = sums each clients total payments $
qryTotalOrders = sums each clients total orders $

I have checked the values in both these qry's and they look correct.  The qryOutstandingAmount that I am having trouble with uses a join to linkboth qryTotalPayments & qryTotalOrders.  The join type only includes rows where the joined field is equal.

The basic formula is

AmountOutstanding = qryTotalOrders!total - qryTotalPayments

The problem is the qry returns the values that look correct, ie people who have paid exactly what they have ordered show a $value of $0.00. The problem is if I click the cell that contains the value $0.00 the figure changes to 3.63797880709171E-12.  Why on earth would this be happening? Thanks in advance for any pointers

RJ
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Question by:robjeeves
5 Comments
 
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Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 16813900
what is the data type of the fields payments resp orders?
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Accepted Solution

by:
harfang earned 120 total points
ID: 16813994
Hello robjeeves

This looks like a rounding error. Computers normally do not perform exact math. For example, you can type this in the immediate pane:

    ? 1-(30001/3-10000)*3

And observe that the result is not 0, but 8.88178419700125E-16. This result reflects the fact that calculations are done with a certain number of digits (15 in this case), and that the remaining digits should be discarded.

If both your sums are really just that: sums of currency values without any calculation, Jet should propagate and automatically round the result to 4 decimals. Obviously, this is not the case, so that you should round the result yourself:

    AmountOutstanding = Round( qryTotalOrders!total - qryTotalPayments, 2 )
    AmountOutstanding = CCur( qryTotalOrders!total - qryTotalPayments )

It would probably be best to revise your queries (and perhaps even your data) to ensure they all have the currency type, or  convert any calculations to currency.

Good luck!
(°v°)
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Expert Comment

by:nharbour
ID: 16815586
AmountOutstanding = CCur(qryTotalOrders!total - qryTotalPayments)
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Assisted Solution

by:Arthur_Wood
Arthur_Wood earned 80 total points
ID: 16815742
just so you understand that what you are getting is NOT an error, the value you are seeing

3.63797880709171E-12

is the same as 0.00000000000363797880709171

which is very close to 0.00 , and the reason is undoubtedly round-off error, as explained by harfang.

AW
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LVL 9

Author Comment

by:robjeeves
ID: 16829316
Thanks guys, I used the round formula suggested and it works a treat.  Most appreciated !!!
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