The uptake of foliar-applied metal ion nutrients, for example, zinc, iron, magnesium and copper, is influenced by humidity. The spring clip portion includes two opposed electrical contacts at least one of which is resiliently biased toward the other. To qualify a deal from the inventory of candidate deals, the method may quantify one or more parameters of a candidate card deal. During simulation of the test vectors, manually generated tests or automatically generated checkers can monitor portions of the circuit for defective behavior. The extension unit includes an extension body and a tongue extending from the extension body.