Primary and secondary quantities dimensional constants

3 Primary and Secondary (Derived) Quantities Dimensional Constants A distinction is made between primary or base quantities and secondary quantities derived from them. The base quantities are based on standards and are quantified by comparison with them. The secondary quantities are derived from the primary ones according to physical laws, e.g. velocity = length/time. All secondary measuring units must be coherent with the base units, e.g. the measuring unit of velocity must not be miles/hr or km/hr but m/s  

Basic quantity basic dimension basic measuring unit  

A further example is the universal gas constant R, the introduction of which ensures that in the perfect gas equation of state pV = nRT the secondary unit for work W = was not violated. 

Another class of derived quantities is represented by the dimensional coefficients in the transfer equations of momentum, mass and heat. These are so-called definition quantities , established by the respective physical equations and are only determinable via measurement of their constituents. 

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