On 2021-09-03 16:13, Chris Angelico wrote:
On Sat, Sep 4, 2021 at 12:08 AM o1bigtenor <o1bigte...@gmail.com> wrote:
Hmmmmmmm - - - ZI would suggest that you haven't looked into
taxation yet!
In taxation you get a rational number that MUST be multiplied by
the amount in currency.
(You can, of course, multiply a currency amount by any scalar. Just
not by another currency amount.)
The error rate here is stupendous.
Some organizations track each transaction with its taxes rounded.
Then some track using use untaxed and then calculate the taxes
on the whole (when you have 2 or 3 or 4 (dunno about more but
who knows there are some seriously tax loving jurisdictions out there))
the differences between adding amounts and then calculating taxes
and calculating taxes on each amount and then adding all items
together can have some 'interesting' differences.
So financial data MUST be able to handle rational numbers.
(I have been bit by the differences enumerated in the previous!)
The worst problem is knowing WHEN to round. Sometimes you have to do
intermediate rounding in order to make something agree with something
else :(
But if you need finer resolution than the cent, I would still
recommend trying to use fixed-point arithmetic. The trouble is
figuring out exactly how much precision you need. Often, 1c precision
is actually sufficient.
At some point, some finance/legal person has to specify how any
fractional currency should be handled.
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