When Johnathan Hottell from filear.com was developing some programming for his PLC testing how things work was often not very easy. The PLC IO Simulator allows Johnathan to simply adjust value on the simulator to see what happens on the PLC logic. Turning a potentiometer is a bit simpler than draining a 100 gallon tank to see what happens in the PLC. The wiring is actually quite nice based on the volume of conductors in the project box.