Abstract: A test device (40) has a patterned conductive layer (42 or 44) particularly adapted for use in an E-beam probe system (FIG. 3) to study how local electric fields influence probe voltage measurements. The layer is composed of two or more conductors (A and B.sub.J C and D.sub.J) separated from each other. Each conductor has a group of fingers. The fingers (F1.sub.p, F0.sub.p, F2, F0.sub.Q and F1.sub.Q) run parallel to one another and are at least partially interdigitated. The width of each finger is constant along its length. The widths of the fingers and the spacings between them vary from finger to finger according to a selected pattern.