In the discussion of current detection its interesting to talk about another method of current detection: the Langmuir Probe.
Langmuir Probe: This device measures current in plasma, it is basically a third electrode stuck into a gas discharge tube. The difference between the current detected in the Langmuir Probe and the plasma space potential can tell you the ion and electron densities of the plasma. More >
While the Langmuir Probe is not an “ammeter” it is an example of how Unit I of this series (Ammeters, Voltmeters) form the foundation for other rather spectacular and complex instruments.