Moshe Gerstenhaber and Mark Champion write:
Numerous applications require the measurement of very low resistances, including but not limited to fuse integrity analysis, relay characterization, and superconductor evaluation. There is a wide range of commercially available equipment designed for this task, but these units are prohibitively expensive and cannot be practically integrated into many applications outside the laboratory. A common low-cost and compact method of measuring resistance is to inject a known dc current into the unknown resistor, measure the resulting voltage and calculate the resistance using Ohm’s law. Unfortunately, for very low resistances, the current required to generate a voltage sufficiently distinguishable from the surrounding noise becomes impractically large.
Complete, low-cost, software programmable ohmmeter measures micro-ohms – [Link]