product payment devices upon the suitable selection or specification of device parameters to ensure proper functioning of a product reader e g pcd r with a product card e g picc c a paypass u2014 reference picc is used to generate a range of behaviors f 2 x f 3 x in a function f of variable x the function f may for example be a magnetic field response as a function of distance this range of behaviors f 2 x f 3 x is observed on a paypass u2014 reference pcd see fig3 the paypass implementation may require or specify that a product card i e picc c must display a behavior fc x that falls within the range of established card behaviors f 2 x f 3 x to be u201c compliant u201d the behavior fc x is observed on the paypass u2014 reference pcd see fig4 further the paypass implementation may require or specify that a product reader i e pcd r must function correctly with the paypass u2014 reference picc exhibiting a range of card behaviors f 1 x f 4 x as observed on the paypass u2014 reference pcd to be u201c compliant u201d by requiring or specifying that the range.