Various methods of inspecting a workpiece for residue are provided. In one aspect, a test structure is provided that includes a substrate, a first conductor on the substrate and a second conductor on the substrate. A resistor network is coupled in parallel between the first conductor and the second conductor. The resistor network has n resistors and n contacts and a measurable resistance RM. Each of the n resistors has a known resistance Rk and a known position on the substrate. Each of the n contacts is connected between one of the n resistors and the first conductor or the second conductor, whereby the location of any of the n contacts in an open state is determined from the equation: R M = 1 1 R k + … ⁢   ⁢ 1 R n The test structure provides for not only the identity but also the location of open contacts.