Abstract: Apparatus for analyzing electrical circuit boards by measuring the voltage drop due test currents flowing along a conductor to an IC mounted on a circuit board, comprising a probe having at least two contact tips mounted to simultaneously contact at least two points on the conductor, the tips being spaced apart sufficiently to permit measurement of electrical activity in a segment of the conductor between the tips, and means for injecting a test signal directly into the conductor via the probe, improved in that there are provided means for measuring a first voltage drop across a segment produced by the flow of test current through the segment away from the IC and a second voltage drop across a segment produced by the flow of test current through the segment into the IC, and means for determining the ratio R.sub.1 /R.sub.2, where R.sub.1 is the internal resistance of the IC and R.sub.2 is the parallel resistance of all other ICs on the same node.