Well document your code!
Parts purchase order form with unique invoice number. This is for the customer service person to use online to enter information from phone customers.
Customer number, Name, address, city, st, zip, phone, email, shipping adress, city, st, and zip.
Part Number, quanity, price and total.
Parts must automatically multiply qty x price = total / then add totals together x tax = grand total.
Name on Card, Card number, card type, exp date and three dig code.