methods and apparatus utilizing a posteriori adjustments to a projection imaging machine used in manufacturing of semiconductor integrated circuits are described . measurements of degradation in a lithography processing of a projection imaging tool or machine are provided . the operation of the projection imaging tool is adjusted in response to the measurements . the projection imaging machine or tool can be adjusted in a single adjustment , or in a series of sub - adjustments . likewise , only a single machine may be adjusted , or multiple machines used in the manufacture of semiconductor integrated circuits may be adjusted . the measurements may be made using in - situ metrology tests . a database including historical and current machine states may be utilized in determining degradation of the lithography processing .