I should have mentioned. When measuring signal strengths as a measure of
performance there's safety in numbers. Take the average of a fair number of
transmissions, all well above the noise level, at about the same time each
day, using your most stable S-meter with the receiver gain turned down such
that the meter deflection is on the most sensitive sector of its scale.
Allow the receiver to warm up for the same length of time on each occasion
it is used.

S-meter calibration doesn't matter two hoots.

And once set, don't ever touch the receiver gain control.

You should take all these precautions from the time when you have laid only
one radial. You will not wish to dig up already laid radials in order to
re-measure the earlier ones you forgot to treat in the standard manner.

It will be appreciated, to make tests during radial-laying operations by
asking for signal strength reports from your many friends, using THEIR
S-meters, will result in you losing them.

Incidentally, when "I" used this method of testing antenna efficiency I
stopped at 8, 10 feet, radials with a 3 feet rod at the end of each. This
included the domestic incoming main water pipe which made no difference when
THAT was connected. So I stopped.

But my soil resistivity is only about 70 ohm-metres. I can grow anything in
my garden. At present it is covered with a dense growth of 3 feet high
weeds except for a small patch which I use to feed the birds. As if they
didn't get enough to eat anyhow. With the trees and overgrown bushes it is
a wild-life sanctuary for frogs, rats, squirrels and hedgehogs. The only
complaints I get are from the neighbours. But its stopped them complaining
about TVI.
---
Reg, G4FGQ