The Minimal Set of Basic Fundamental Units

Prefix Abbreviation Power Prefix Abbreviation Power 

The ideal gas law provides a relation between temperature and the product of pressure and volume. However, a conversion factor R is needed. Instead of making use of the conversion factor, we can state directly 

In this view, T has the dimension of energy per mol. We could readily measure the temperature in terms of volume and pressure - if an ideal gas is available. So we have traced back the temperature to the (mean) energy of a particle. The temperature is expressed in terms of mechanical quantities. 

In a similar way as shown for the temperature, also other physical quantities even belonging to the so-called basic or fundamental units can be traced back to mechanical physical quantities. It remains to answer how many basic units are really needed at minimum. First, we state that the introduction of a physical unit requires the definition of a physical quantity itself. Without a physical quantity now unit for this quantity is needed. The new physical quantity is introduced by a relation including other previously known physical quantities. 

In fact, the question arises whether we need really these seven basic units, or whether the number of basic units can be still fiuther reduced. For example, around 1900, Oswald suggested that the energy should be one of the basic units. Instead 

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