Virtual earth for measuring small currents.
Most multi-meters are not sensitive enough to detect low uA and have a high shunt resistance which can affect the circuit under test.
This circuit will adapt a voltmeter to measure between 1uA and 9mA when using a pair of 9V batteries for the op amp. it is 1:1000 Amps:Volts (Inverted)
The diodes provide protection by clamping any current surges that exceed the capabilities of the circuit.
