Method of detecting spatially correlated variations in a parameter of an integrated circuit die

A method of detecting variations in a spatially correlated parameter comprising:

• measuring a selected parameter of each of a plurality of electronic circuits replicated on a common substrate;
• calculating a difference between a value of the selected parameter at a target location and that of an identical relative location with respect to the target location for each of the plurality of electronic circuits to generate a distribution of differences;
• calculating an absolute value of the distribution of differences;
• and
• calculating an average of the absolute value of the distribution of differences to generate a representative value for the residual for the identical relative location wherein the common substrate comprises a plurality of common substrates wherein best estimates for a given X-Y location are identical to those of a corresponding location on another of the plurality of common substrates.