An apparatus and method for detecting mispositioned wafers attributable to transfer shift of the wafer are disclosed. A calibration wafer has a target region comprising a pattern of optically distinguishable features from which is determined the position of the calibration wafer within the chamber subsequent to its transfer therein. Preferably, the features comprise a pattern of colors that can be detected by spectroscopy. A preferred form and manner of providing such color features is by way of dielectric thin film filters.