In 1940, Harvard psychophysicist S. S. Stevens initiated the theory of measurement scales defining a scale according to The transformation group conserving the scale and the scale's ALLOWABLE STATISTICS. It's scandalous that The National Bureau of Standards and physics departments around the country have not adopted any system this well-founded!

MEASUREMENT SCALES TABLE

SCALE	PROTOTYPE	TRANSFORMATION GROUP	ALLOWABLE STATISTICS	EXAMPLES
Nominal	Personal name	"ID"	Mode(s)	Proper names; technical terms
Typological	Family name	Identity function	Mode(s)	Taxonomy of plants and animals; etiology of diseases
Ordinal	Preference	Isotonic	Median; range	Moh mineral hardness scale; IQ; Richter-Kanamori earthquake scale
Interval	Temperature scale	Linear	Arithmetic mean; variance	densities;Celsius & Fahrenheit temperature scales
Ratio	Weight	Similarity	all statistics	length, area, volume, etc.