By dowsing the location in question, which is the same technique used by many militaries and water authorities to find water in the underground.
One can often deduce the influence of GS and ES by the ailments and symptoms that people and animals experience.
Also, many health practitioners measure the presence of Geopathic Stress or Electro Stress in their patients with common diagnostic equipment like VEGA or MORA machines.
Some characteristics of electromagnetic fields, but by no means all, can be measured by electronic meters. For example, at different locations in the field one can take readings of potential difference in Volt/Metre or the magnetic field strength in Gauss. Readings with such meters merely scratch the surface, so-to-speak, in understanding what these fields can do to human cells and the energetic systems present in every human being, without which we could not function.