[GNC] Rounding & formulas

[David Carlson]

I think this rounding problem (if you want to call it that) is not unique
to Gnucash.  You would see the same thing if you were using a spreadsheet,
for example.

For the particular type of example given, it might make sense to track
running totals and calculate monthly amounts required to make those running
totals balance to the desired formula.  This would ensure that there was no
cumulative error from rounding.

On Mon, Dec 21, 2020, 9:12 PM Adrien Monteleone <
adrien.monteleone at lusfiber.net> wrote:

> Or just correct a single digit as desired upon review when the
> transaction is created? (on the off chance the original sum is an odd
> number, which isn't always, and if I recall correctly, this is a *one
> time per month* transaction, thus from 1 to 12 times *per year* the
> transaction won't magically round as desired.)
>
> Regards,
> Adrien
>
> On 12/21/20 5:12 PM, Dale Alspach wrote:
> > I think the problem is that with late rounding the formula may not work.
> > Suppose the amount is 0.21.
> > Compute amount/2 exactly: 0.21/2=0.105
> > Subtract from amount 0.21 - 0.105=0.105
> > For a fixed rounding scheme both will either be 0.11 or 0.10 and the sum
> > will be 0.22, respectively, 0.20. Neither is the desired 0.21.
> >
> > If the sum is to be correct, one could try to implement amount1 =
> > round(amount/2). amount2 = amount - amount1.
>
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