A machine readable assaying system including an assay card having a machine readable assaying indicia located upon a surface of the card. In one embodiment, a method of monitoring performance of an ME includes receiving a control frame via the ME. Basically, most PCL techniques rely on comparing signal sources with their reflections from an object in order to determine the location of the object. The layer of VSD material may be positioned to protect one or more components of the substrate from the transient electrical condition.