The Requirements of a Standard of Measurement

IIn the words of Ayn Rand: "measurement is the identification of [...] a quantitative relationship established by means of a standard that serves as a unit."^[1]

The "standard" in such a case is something like inches, or lbs, or dB, etc. This standard is subject to an act of choice--reality does not impinge upon us whether to use inches or meters--but there are requirements for such a standard to be rational:

1. the standard must represent the appropriate attribute---one cannot measure pressure with grams or velocity with inches;
2. the standard must be graspable by direct perception within the appropriate context---in determining the distance you must walk in the rain to get from your car to the front door it is ill-advised to use lightyears instead of feet or meters, and;
3. the standard must be immutable once selected---if kilograms refers not to some specifically specified mass but rather a different mass selected arbitrarily upon each new measurement, then it becomes impossible to perform calculations with it.

This is key to understanding why, on Objectivism, a standard though freely chosen is not in any way "subjective"---any rational unit refers to some specific concrete in reality that is what it is independent of any act of consciousness. Measurement and mathematics are not tasks performed by detaching one's cognition from reality and considering some Platonic super-reality---they are and must be rooted in the apprehension of this world.