1. A method comprising: receiving measurement values of one or more specimen parameters associated with a model based measurement of one or more metrology targets by a target measurement system; receiving reference measurement values of the same one or more specimen parameters associated with a measurement of the same one or more metrology targets by a reference measurement source that differs from the model based measurement of the one or more metrology targets by the target measurement system; and determining one or more parameters of a meta-model that transforms the measurement values of the one or more specimen parameters to corrected measurement values of the one or more specimen parameters, wherein the determining of the one or more parameters of the meta-model involves minimizing a difference between the reference measurement values and the corrected measurement values of the one or more specimen parameters.