PME or TT or Both To Caravan Or Outbuilding

[Ian1981]

You are contradicting yourself.
You say it is treated as the electrode resistance, which is fine, but this does not make it Ra.
Ra is a defined quantity, the method you describe results in an approximation, not a measured value, of Ra.

You might as well be stating that g is 10 or that c is 300,000,000
Both are approximations and not the actual values.

Whatever you say dave.........