Re: rounding problems

[Justin <justin@xxxxxxxxxxxxxxx>]

Tomasz Ostrowski wrote:

On 2008-05-12 20:49, Justin wrote:

  

We take (List Price * discount Percent) * Number of Pieces = net
price.
    

This is wrong. You should do in Excel:
( price * amount ) * discount
As otherwise any small error in representation of price*discount would
be multiplied by usually high amount.
  

Your saying in Excel,  Multiplication is not  Commutativity???  that sends shudders  down my back

I'd do this way to get it right:
round( round(price * amount, 2) * discount, 2)
This way every sum should match. There could be errors, but in pennies,
not dollars. These errors will be because Excel does not have a decimal
type.
  

That makes sense you are keeping the precision the same through the calculation

It is a lost case to break Postgres so it will match Excel. Much easier
would be to correct Excel spreadsheet. And this is a right thing to do.

Regards
Tometzky