Circuit level probing is testing, measuring, or characterizing the operation of an electronic circuit. It reveals the true operation of a circuit, and takes the next step beyond electrical engineering design and circuit simulation. This paper presents the return of circuit level probing in nanoelectronics by means of SEM based nanoprobing. It provides information on the process of characterizing resistance matching, diode matching, Op Amp offset matching, and mirrored current. Circuit level probing, using a SEM based nanoprober, identified the problem to be poor matching between the current mirror devices in the circuit. A family of curves device characterization was obtained from the circuit level probing. Discrete devices testing showed good correlation back to the circuit level data. The device mismatch was determined to be associated with the "as processed" built-in potential of the devices, with no abnormal influence from either the gate or drain electrical fields.