Health Check Machine

At the hospital I work, there is a machine in the main foyer which gives one an instant health check. It measures your weight and height and then calculates your body mass. It also takes your pulse and asks you how much fluid you drink in order to work out your hydration levels.

I notice that some people take their shoes off before using it, while other people keep their shoes on. There is no sign to indicate what one is supposed to do, but I would have thought one's shoes would affect the weight it registers.