In the 1933 Bohr and Rosenfeld’s famous article on electromagnetic field measurements they did not consider the measurement of a magnetic component in a given space‐time region, nor the measurement of two parallel magnetic components, nor the measurement of two non‐parallel magnetic components, nor the parallel measurement of one magnetic and one electric component, nor the non‐parallel measurement of one electric and one magnetic component, nor the non‐parallel measurement of one magnetic and one electric component in two different space‐time regions. This article covers the first one of these pending matters.