The Key role of Giovanni Giorgi in Developing the MKSA System of Units

The International System of units used nowadays in most of the word experienced a turning point in the first half of the XX century with the introduction of the ampere (A) as a fourth unit in addition to the original length (M – meter), mass (K – kilogram) and time (S – second), hence turning from a MKS to a MKSA system. This addition was a non-trivial and lengthy process mainly carried on by the Italian engineer Giovanni Giorgi. This contribution retraces this revolution in the measurement system.