²²In an effort to alleviate this confusion, the Allen-Bradley corporation (Rockwell) uses the terms examine if closed (XIC) and examine if open (XIO) to describe “normally open” and “normally closed” virtual contacts, respectively, in their Ladder Diagram programming. The idea here is that a virtual contact drawn as a normally-open symbol will be “examined” (declared “true”) by the PLC’s processor if its corresponding input channel is energized (powered by a real-life contact in the closed state). Conversely, a virtual contact drawn as a normally-closed symbol (with a slash mark through the middle) will be “examined” by the PLC’s processor if its corresponding input channel is de-energized (if the real-life contact sending power to that terminal is in the open state). In my experience, I have found this nomenclature to be even more confusing to students than simply calling these virtual contacts “normally open” and “normally closed” like other PLC manufacturers do. The foundational concept for students to grasp here is that the virtual contact is not a direct representation of the real-life electrical switch contact – rather, it is a read instruction for the bit set by power coming from the real-life electrical switch contact.