Learn in the textbookData Operations and Levels of Measurement
DefinitionA ratio scale (比例尺度) (ratio-level scale (比率尺度)) is a scale that, besides having equal intervals, has a 0 meaning no quantity, so the ratio of values is meaningful too.
ExplanationLength, weight and amounts of money are examples. Because 0 is fixed as the state of having none, 60 kg can be called twice 30 kg, and the results of multiplication and division are meaningful. Of the four scales, its values carry the most information.
AnalogyA wallet holding 0 yen really has no money in it, and 2000 yen lets you spend exactly twice as much as 1000 yen.
Memory hookThe name comes from ratio: this is the scale on which a ratio of two values makes sense.