Macro that will calculate results based on data from other sheets

Hi, I help to create some macros. Currently, I have three worksheets in excel 07. One WS is the main page for displaying all the information that i wanted, another WS is for the products and lastly one for customers.

I need to write a macro that will be able to calculate and display the current amount of products.

The macro will be able to find out the current number of products based on the original amount of products (in the product sheet) removing the amount of products in the customer's orders (in the customer sheet).

This amount will be constantly updated based on the customers' orders that will be entered. I hope I make sense with this. Thanks in advance

Hi dave. Thanks for the response. I've come up with something simple Is the layout of the workbook fine?