Formula for calculating total price - Repost -- 2

I want to integrate a formula (already developed) from Oscommerce to be integrated in Prestashop. This formula calculates in real time the price based on measures, only applies to some of the products of the shop so: 1. Every time a product is created it has to have the checkbox in the backoffice for applying the formula for that product. This product will have only one price (square meter price) and based in that price if the client change the measure, the final quote price will appear and will be added to the cart. 2. Remember that its a question of transferring the formula and adding an option in the backoffice for using it in the front office. Example of one product that should have the formula applied: [login to view URL]