Also, my price is per square metre and the width & length are entered in millimetres for accuracy. This results in a price * 1,000,000. I could change the product price to reflect this but that would be messy so I changed the calculation in the plugin to
$product->order_product_total_price_no_vat = $product->order_product_price*($quantity/1000000);
$product->order_product_total_price = (($product->order_product_price+$product->order_product_tax)*($quantity/1000000));
Apologies if this is complete nonsense in code terms, I can see where the change is required but I'm a novice. The change has had no effect. Basically I need to convert the quantity to mm therefore divide by 1,000,000. Please advise. Thank you for your help.