Calc or Auto Calc field?

[raymanj]

I am trying to determine if it is better to use a calculation field or a auto enter field for this particular situation.

Situation:

Invoice system, invoice table and line items table. Each line item has a set of fields item number, quantity, description, price, discount and extended amount. Now, what would be better for an invoice system, to use a calc or auto enter for the extended amount field?

Could anyone give some advice on this?

Thanks

[MoonShadow]

The Extended Amount field can be in LineItems, which takes Quantity times Price. This can be an Auto-Enter (standard number field) by calculation (Replace existing values). To derive the sum of your LineItems for your Invoice total, you will need to use Sum() which can not be stored and must be a calculation.

[comment]

IMHO, auto-enter should be used when a user is expected to enter something into the field. Then either user input overrides the calc, or, if "Do not replace ..." is unchecked, the calc overrides user input - but still using the input (e.g. phone number formatting).

Example:

Customer bought 5 items @ $10 each. Auto-enter ExtendedPrice says $50. Customer haggles. Seller agrees to a discount, and enters $45 into ExtendedPrice.

However, this is an example of bad practice: upon review, there is no trail of what really happened, and 5x10=45 looks like a mistake. Much more sensible to have a separate field for overriding price, or discount (as you have). Then there is nothing for the user to input into ExtendedPrice, and it can be simply a calculation field.

[raymanj]

Thanks for the reply, but what I am really looking for is it better to have the extended amount as a calculation or as a auto enter field. My invoices will have many line items per invoice (100 or more). So speed is a concern. Also looking at an invoice system from the data collection view point, is it better to store these values (auto enter) or keep them as unstored calculations.

My main question is should they be stored or not.

Any advice from people that have dealt with invoice systems for companies and their concerns on data integrity.