Measurement data sets for optical metrology systems can be processed in parallel using Multiple Tool and Structure Analysis (MTSA). In an MTSA procedure, at least one parameter that is common to the data sets can be coupled as a global parameter. Setting this parameter as global allows a regression on each data set to contain fewer fitting parameters, making the process is less complex, requiring less processing capacity, and providing more accurate results. MTSA can analyze multiple structures measured on a single tool, or a single structure measured on separate tools. For a multiple tool recipe, a minimized regression solution can be applied back to each tool to determine whether the recipe is optimized. If the recipe does not provide accurate results for each tool, search parameters and/or spaces can be modified in an iterative manner until an optimized solution is obtained that provides acceptable solutions on each tool.