Method for measuring at least one target on a substrate

Disclosed is a method of determining a correction for a measurement of at least one target on a substrate, the target comprising one or more parameter of interest sensitive sub-targets which are each sensitive to a parameter of interest and one or more parameter of interest insensitive sub-targets which are substantially less sensitive or insensitive to the parameter of interest, the method comprising. The method comprises obtaining a respective first measurement parameter value relating to each of said one or more parameter of interest sensitive sub-targets; obtaining a respective second measurement parameter value relating to each of said one or more parameter of interest insensitive sub-targets; and determining a correction for each said first measurement parameter value using said second measurement parameter values and/or detecting the presence of an effect likely to impact accuracy of first measurement parameter values from said second measurement parameter values.