An absolute scale is a system of measurement that begins at a minimum, or zero point, and progresses in only one direction. An absolute scale differs from an arbitrary, or "relative," scale, which begins at some point selected by a person and can progress in both directions. An absolute scale begins at a natural minimum, leaving only one direction in which to progress. This natural minimum must be an intrinsic property of the measured dimension rather than a natural side-effect of its progression (i.e.: Water freezes and boils naturally at certain temperatures, but these are not natural minimums or maximums of temperature.)