Nominal: If the variable is not ordered and only uniqueness matters. An example is the country of origin or the id.
Ordinal: If the variable is ordered (smaller, larger). An example is the safety rating.
Interval: If the variable is ordered and the relative magnitude of the variable has a physical meaning. The year is interval since the dierence between say 82 and 85 (three years) has the same meaning as the dierence between years 77 and 80, however the safety rating is not interval since a dierence in safety rating of 2 and 4 and 3 and 5 does not have a physical meaning.
Ratio: If the value 0 of the variable has a specic, physical meaning. I.e. it makes sense to say one value of the variable is \twice as large" as another. The year is not ratio since it has no particular meaning to say that 62 is twice as large as 31, whereas the volume of the engine does have a particular physical meaning since a value of 0 means the combustion chamber has volume 0 cm3.
Military rank: Discrete, Ordinal
Angels in degrees: Contioneus, Ratio
A persons year of birth: Discrete, Interval
A persons age in years: Discrete, ratio.
Coat check number: Discrete Nominal
Distance from center of campus: Continous, Ratio
Number of patients in a hospital: Discrete Ratio