Scales organized by transformations under which the meaning remains invariant. Based on sets Objects classified by shared attributes. All members belong equally. Examples based on a footrace. Differences between two interval measures are ratio.
Interval measures are often raw results, with some additional relationships they become ratio.
May be rescaled because '1' is arbitrary. In 1959, Stevens recognizes that the invariance rules could allow another scale on the same 'level' as interval. Beyond Ratio Ratio is not the 'highest' level of measurement, '1' need not be arbitrary. Using Stevens' invariance scheme, an 'absolute' scale could not be rescaled by any multipier. Both zero AND one are fixed.