Royal Society of Chemistry

Table 1.1

Generic concept system on ‘property’. The letters a, b, c, and d signify individual properties in comparisons; n is a numerical factor.

Type of property	Allowable comparison	Example
nominal property	a = b a ≠ b	colour
quantity
ordinal quantity	a < b a = b a > b a ≠ b	octane number
unitary quantity
differential (unitary) quantity	\|a − b\| = \|c − d\| \|a − b\| ≠ \|c − d\|	Celsius temperature, pH
rational (unitary) quantity	a = n ×b a ≠ n × b	mass, thermodynamic temperature

Type of property	Allowable comparison	Example
nominal property	a = b a ≠ b	colour
quantity
ordinal quantity	a < b a = b a > b a ≠ b	octane number
unitary quantity
differential (unitary) quantity	\|a − b\| = \|c − d\| \|a − b\| ≠ \|c − d\|	Celsius temperature, pH
rational (unitary) quantity	a = n ×b a ≠ n × b	mass, thermodynamic temperature