The half-cell is not a reference electrode.

I have been told by highly qualified scientists that is it not even a half-cell
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http://www.rogeralexander1938.webspace.virginmedia.com/cpn/halfcell/halfcell.htm
...

The link shows pictures that prove that the copper/copper-sulphate electrode is merely a suitable ground contact.

Cathodic Protection Network Master Class

How to control corrosion in pipeline systems.

It has been suggested that I hold a 3 day master class for Cathodic Protection Network technology and it will be a good opportunity to explain the significant changes that are presently happening  to the whole of the cathodic protection industry.

This is a scientific and technical blog

Please keep opinions to the minimum and base postings on facts that are established by repeatedly demonstrable observations that you are prepared to support with documentation, pictures mathematical calculations etc.
Scientific papers and some codes of practice contain words and characters derived from Greek and Latin and are not in general use by the people who have to apply the advice they advocate.
Cathodic Protection Network is a facility to bridge the gap between the elite academics and the people who walk miles over pipelines gathering data and noting crucial information.

International reference potential

When we make voltage measurements pertaining to two or more pipelines we have to relate these to a reference potential in a fixed position so that we can understand the direction of flow of electrical currents.
Corrosion committees are already required by law to mitigate interference corrosion between pipeline owners and their measurements must relate to a common potential to make any sense.  There are no boundaries to pipeline networks and we therefore need a common reference potential in the same way that we need the conventions on international time.

Attenuation curves

Pipe-to-soil voltages graphs are sometimes called 'attenuation curves'. They are similar measurements to those we make when carrying out close interval potential surveys and are ground potentials

The very word 'attenuation' infers that it is the pipe metal potential that varies and this is
incorrect. Could one of our NACE or Institute members please explain this?

Criterion for cathodic protection

It can now be demonstrated that the copper/copper-sulphate electrode cannot be regarded as a fixed potential against which a voltage can be measured for cathodic protection survey work.  This raises the question of interpretation and analysis of the millions of voltages that have been recorded over the years and are still being recorded world wide.
It is clear that there can be no criterion for the achievement of protection using a voltage that is measured between to floating potentials.  The established way of presenting this is a straight line at -0.850 volts on a graph showing distance X and voltage Y but if both potentials are floating then the -0.850 volts is also floating.
What is needed is a corrosion cell that can be monitored at each location as close to the pipeline or structure as possible.  The arrangement of coupons that is called the Alexander Cell is just this.
This will show the actual electrical equilibrium at which corrosion stops and can be related to the pipe-to-soil voltage taken at the same spot.