Framing Mount Surcharge

Internal object — not a retail product. Carries the conservation-mount surcharge that accompanies a framed poster. Added automatically by the product page when a customer selects Add Mount; it is never bought on its own. The surcharge is 20% of the selected framing charge, rounded to the nearest £5 with an exact midpoint going up. Each cart line is linked to its parent poster by a hidden _po_link property. Do not publish, merchandise, discount or delete without checking the Phase D record.