Presenter notes: Write three numbers on the board with nothing else: 37, 98.6, 310. Ask what they have in common. Nobody will get it. Tell them these are three names for exactly the same thing, which is the temperature of everybody sitting in this room right now. Then ask the obvious question: why would anybody need three different numbers for one temperature? By the end of the period they will be able to convert between all three, and more usefully they will know why the formula looks the way it does instead of having to memorise it.