Data is classified into four levels of measurement. The ratio level of measurement is an extension of the interval level of measurement. It deals with data that have a natural zero point. The difference between the values, and the ratio of values, both are meaningful in the ratio level of measurement. For instance, a statistics book may cost 50 dollars and a comic book 5 dollars. This is countable data, can be ordered as expensive or cheap, and the difference between the values is also meaningful. The statistics book costs 45 dollars more than the comic book. It also has a natural zero point – zero dollar means no cost. Additionally, the ratio between the values is also significant – the price of the statistics book is ten times that of the comic book.