Testing and characterizing metallic materials, low temperature superconductors, nanoscale materials, highly doped semiconductors, photo-diode dark currents, and electron beam currents from accelerating devices requires making current measurements at nanoamp levels and below. Either the generated current is low or very low power materials, such as single-atomic-layer graphene, must operate with very low currents to minimize power dissipation and destruction due to self-heating. Similarly, high resistance measurements on insulators, polymers, ceramics, and lightly doped semiconductors also demand the ability to measure very low currents.