Can anyone recommend a good book on developing efficient
access forms that can perform calculations and save such
calculations in the underlying table/s
No such book exists, because no professional designer would do such a
thing except in very rare circumstances.
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.
Could you explain the *real life problem* that you are trying to
solve? It's surely soluble - but storing calculations in the table is
not likely to be the best way to solve it!