What is scale interval?

Answer 1

An interval scale is a scale of measurement for which the difference between two points on the scale is meaningful. The scale gets its name because this definition implies that the intervals between successive points on the scale are the same.

For example, the Western-style calendar years form an interval scale. The distance between 1901 and 1902 is the same as the distance between 2032 and 2033, namely one year. At the same time, the distance between any pair of years, for instance, 1066 and 1075 is also meaningful, being 9 years.

However, it's important to point out that, although there is a '0' year we cannot say that the year 2000 is 'twice as old' as the year 1000.