That is where the measuring starts. With a ratio scale we can say that one point on the scale is so much more or less than another. 10 centimetres is twice 5 centimetres and half of 20 centimetres. We cannot do this with simple interval scales. The year 1998 is not twice a previous year or half of a future year.
Ratio scales are real numbers .
They have order , equal intervals and an absolute zero. It is because real numbers have these characteristics that we can perform the operations of mathematics with them. Real numbers and ratio scales can be added, subtracted, multiplied and divided. They can also be raised to powers or brought down to roots , and this means that we can take logarithms and use calculus with them. It is one of the great discoveries of mathematics made in India.