Teams usually use the number of pieces to demonstrate compliance, though cost is an acceptable approach. If you have several relatively inexpensive pieces of non-compliant equipment and one very expensive compliant piece, it may make sense to run the numbers to see if you meet the 20% threshold by cost, if you can’t meet it by number of pieces. If you don’t have cost data for existing equipment and you want to demonstrate compliance by cost, work with suppliers that carry the equipment to gather the cost data.