class ZbsCartCalculation { 
  public function __construct($shipping_zone){ 
    // creates a cart calculator for a zone 
  } 
 
  public function add_product(  
      $product_name, 
      $product_quantity,
      $product_price_to_pay,
      $product_weight_units,
      $product_dimension_units,
      $product_weight,
      $product_length,
      $product_width,
      $product_height,
      $product_shipping_modifier,
      $product_requires_shipping,
      $product_shipping_measure_attribute )
    { 
    // accumulates cost of items added 
  } 
 
public function cart_complete () { 
  // returns the accumulated cost and delivery message 
}