Ratio scale - true zero point as the origin

Ratio scale: These represent the strongest level of measurement. In addition to providing ranking and equal differences between scale values, ratio scales have a true zero point as the origin. I don’t understand last line “true zero point as the origin”, what does it mean? Could anyone clarify with example pls. Thanks,

Here’s my perception: zero, under ratio scale, has no value. for example, $0 means no dollars. however, zero degree celsius doesn’t mean there’s no temperature to measure.

I dont have my book in front of me, but i think it implies that once you can perform operations on the numbers, you establish a relationship between some point, in this case zero. Mean, std dev for example, creates a scale that uses zero as its origin (true mean minus sample mean) and dispersions from the mean. This is just a stab at it though.

Some scales of measurement have a natural zero and some do not. For example, height, weight etc have a natural 0 at no height or no weight. Consequently, it makes sense to say that 2miles is twice as large as 1mile. Both of these variables are ratio scale. On the other hand, year and temperature (C for centrigrades) do not have a natural zero. The year 0 is arbitrary and it is not sensible to say that the year 2000 is twice as old as the year 1000. Similarly, zero C is arbitary temperature(why pick the freezing point of water?) and it again does not make sense to say that 20C is twice as hot as 10C. Both of these variables are interval scale. hope i made sense!

A true zero signifies that the bathroom scale registers 0 when not in use—that is, when weight is completely absent. Since the bathroom scale possesses a true zero, numerical readings reflect the total amount of a person’s weight, and it’s appropriate to describe one person’s weight as a certain ratio of another’s. It can be said that the weight of a 140-lb person is twice that of a 70-lb person.