Calculation script: 

If you write and use your own calculation scripts, then you should always use only the price variables. The priceTax and priceNoTax variables will be deleted in August 2008 because they can be calculated from the price variables and the TAXpercentage and TAXincluded constants. You can use the global PHP variables $this->calculatedArray and $this->itemArray to make your own price calculations.

10.calculationScript = EXT:tt_products/pi1/products_comp_calcScript.inc