The concept of the "geoelectrical trace

Influence of natural time-dependent variations of electrical conductivity on DC resistivity measurements

“…With an interval of 480 ms, the introduced frequency was 24-fold of the public electricity supply (20 ms or 50 Hz), and the eight-fold of the railway electricity supply (60 ms or 16 2 3 Hz). So, these disturbing signals have been eliminated to a large extent by destructive superposition (concept of the geoelectrical trace, according to Dietrich and Fechner (1998)). …”