An apparatus may include a processor and memory unit, including a control routine having a measurement processor to determine, based upon a first set of scatterometry measurements, a first change in a first dimension of a first set of substrate features along a first direction. The first set of substrate features may be elongated along a second direction perpendicular to the first direction. The measurement processor may be to determine, based upon a second set of scatterometry measurements, a second change in dimension of a second set of substrate features along the second direction, wherein the second set of substrate features is elongated along the first direction. The apparatus may include a control processor to generate an error signal when a figure of merit based upon the first change and the second change lies outside a target range.