They want a spreadsheet and not a database then.

You can not do calculations in a table. Further you should not store
calculated data in a table. When you need to see calculations, you should do
if fresh each time in a query, form, or report.

Yes.

Storing derived data such as this in your table accomplishes
three things: it wastes disk space; it wastes time (almost
any calculation will be MUCH faster than a disk fetch); and
most importantly, it risks data corruption. If one of the
underlying fields is subsequently edited, you will have data
in your table WHICH IS WRONG, and no automatic way to detect
that fact.

Just redo the calculation whenever you need it, either as a
calculated field in a Query or just as you're now doing it -
in the control source of a Form or a Report textbox.

Table datasheets are of VERY limited utility. Users should in general not even
*see* tables, much less use them for data interaction.

            John W. Vinson [MVP]