subtracting and updating a field value

[randomtask976]

hello,I am writing an inventory database but I need help with a calculation, I have a field for quantity on hand, and I have field for quantity consumed, what would be the calculation that I need to enter so that qty on hand changes in regards to qty consumed

[bcooney]

I always point Inventory questions to this terrific article by Jonathan Stark.

Inventory systems tend to rely on many unstored calculation fields, and can get very slow. You might look into a transaction system (that is, updating the totals by script rather than by relationship-based unstored calcs). See this article by Todd Geist.