1. A method of determining at least one parameter of an object model used in a device manufacturing process, the object model providing information about a position of an object, the object having a plurality of alignment marks with desired positions that are known, the method comprising: receiving signals from the plurality of alignment marks; determining a strength of the received signals; determining weighing coefficients based on the strength of the received signals; measuring a plurality of positional parameters for the plurality of alignment marks, the plurality of positional parameters being weighted with the weighing coefficients; determining the at least one parameter of the object model based on the measured plurality of positional parameters, including determining a numerical value of at least one of the weighing coefficients the at least one parameter of the object model simultaneously; and using the object model in the device manufacturing process.