My book says that ratio levels of measurement is the highest form of measurement and adheres to the same rules as as interval level measurement (distances between intervals of the scale are numerically equal), but it can have an absent property.
The examples are weight, height, blood pressure, pulse, etc.
How can weight or height be a ratio measurement? What thing being measured for weight has not weight? Or has no height? I understand no blood pressure or pulse.
Thanks :)