> OK - what I have done (to allow the user to update values in
> lookup tables)
> is to write the original value into the primary table when the value is
> inserted into the primary table.
>
> In other words, the primary table now has a "taxrate" field. This field
> holds the tax rate at the time that the record was inserted. In
> this case,
> it will allow the user to update the tax rate field without changing the
> value in records in the primary table.
>
> Is this the kind of thing you mean, Helen?
>

This certainly sounds more logical where transactions are indeed made under
a certain tax regime. If the tax regime changes, the gov would hardly want
to refund and over-payments or (not alsways anyway) want historical
transactions to cough up another margin.
To have done this the original way wouod mean that trasnactions made several
years ago do not now balance.
Alan