You can see the size of 3 of the containers as they are within a clear plastic container.

When making cathodic protection measurements you can only see the readings on the meter and the points of contact of the probes.

We are trying to measure different levels within the model in a similar way that we are trying to measure the difference in electrical potentials in cathodic protection work.

You cannot see size of the glass container on the right as it is buried in sand. As in cathodic protection field work we can only see the ground on which we stand and not the electrical conductors or configuration that lies beneath our feet.