/sci/ - Science & Math

When measuring the vertical position (height) of an object, would you measure it from the top or the bottom? For example, if you are measuring the height of a person in the process of diving into a pool, would the height be calculated based on his head or his feet? Pic related, would the diver's height be 10m or 5m? This is a serious question, I'm not trying to be a baiter like the flies in a jar question, I need to know this so I can make an accurate measurement of height.