Their Fig. 7 shows results of simplified (manual) calculations, not measurement results.
Quoting from page 771 of the BL&E paper on ground systems:
"The current in the buried wires was measured in each case. This was accomplished by placing a coil next to the ground wire at a point where the wire was exposed. The coil was resonated by means of a small shunt condenser. The voltage across this combination was de- termined with a vacuum tube voltmeter. The combination was cali- brated in the laboratory. Fig. 24 shows the procedure in question. This measurement yielded the current in a single wire. To obtain the current flowing in all the buried wires at distance, x, the measured value was multiplied by the number of wires." R. Fry _________________ Topband Reflector Archives - http://www.contesting.com/_topband
