A semiconductor wafer having two regions of different dopant concentration profiles is evaluated by performing two measurements in the two regions, and comparing measurements from the two regions to obtain a reflectivity change measure indicative of a difference in reflectivity between the two regions. The piston actuates the downhole tool, and the primary control subsystem may be connected to at least one hydraulic line in order to move the piston in response to pressure that is communicated to the tool via the hydraulic line. The columns can be treated to enhance mechanical properties such as stiffness, electrical properties such as electrical conductivity, andor physical contact characteristics. One of the first or second distributions is compared to another of the first or second distributions.