These are a couple of examples of things that retail staff may be expected to get involved with, and they'll be keen to see how much additional training they might need to provide.
Three Logic Levels are used and they are High, Low, HIgh impedance state. The high and low are normal logic levels & high impedance state is electrical open circuit conditions. Tri-state logic has a third line called enable line.
Energy can be transferred from one system to the other. The rate at which energy is transferred from one system to other system is called POWER. Energy transferred in one second is called a watt.