I mean even metric is somewhat defined by the world 0°C is the freezing point of fresh water 100° is the boiling point. That's somewhat arbitrary. You could as

I mean even metric is somewhat defined by the world 0°C is the freezing point of fresh water 100° is the boiling point. That's somewhat arbitrary. You could as easily have used saltwater as °F does, the difference in this case is that it's divisible in 10s 100s. The original definition of a kilogram is 1 litre of fresh water (I think they're more precise now), but it still works for common usage. A litre is 10cm x 10cm by 10cm of water (it's metric turtles all the way down) Finally the original definition is where we get to the base arbitrary, it was 1/10,000,000 of the equator to the north pole (it has since evolved, from the 1790s). What's important here is the consistency and ease of use in mathmatical units with everything being in 10s and 100s.