It is natural to think that if a quantity exhibits this degree of freedom in its choice, then it should not be interpreted as a real physical quantity. After all, if we can freely choose ∇ ∇ ⋅ ⋅ A to be anything, then A is not unique. One may ask: what is the "true" value of A measured in an experiment? If A is not unique, then the only logical answer must be that we can never measure the value of A . On this basis, it is often stated that it is not a real physical quantity and it is believed that the fields E and B are the true physical quantities.