Interval scale refers to a measurement scale that possess the properties of difference, magnitude, and equal intervals. Interval scale, moreover, is defined as a scale of measurement in which the categories are organized sequentially and all categories are the same size. The zero point of an interval scale is arbitrary; a scale that one can use to rank order objects and on which the units reflect equivalent magnitudes of the property being measured.
Lexicon of Psychology - Terms, Treatments, Biographies,