Correction to field strength in base.py

[8ung3st]

Trying to match field strength output to Figure 3 of the 2014 ITU "Handbook on Ground Wave Propagation" (here), I came upon the correction applied to the result from grwave.for in base.py (defined in line 14). It results in values being half as high as for the equivalent setup in the handbook. Can you tell me why this factor is being applied?

Also, the y axis on the example graphs are labeled mV/m but negative values are shown. Should that be dB(\mu V/m)?