The article discusses the problems of solving the potential field of earthing conductors of high-voltage electrical installations with an emphasis on the problem of heterogeneity. Weak points in the current method of measuring specific electrical resistance are highlighted, as well as weak points in the equivalence procedure, as well as weak points in calculation and design. Selected examples provide insight into the magnitude of the equivalence error. A numerical method of field calculation is proposed as a basis for measurement and design, relying on the use of a calculator.