Abstract: A method of calculating delay for a process variation includes finding a value for each of exactly two independent variables that results in a maximum or minimum variation of estimated cell delay plus net delay, calculating a variation of resistance from the value found for each of the exactly two independent variables, calculating a variation of capacitance from the value found for each of the exactly two independent variables, adding the calculated variation of resistance to a net resistance to generate a modified net resistance for a selected net, adding the calculated variation of capacitance to a net capacitance to generate a modified net capacitance for the selected net, and calculating the cell delay plus net delay from the modified net resistance and the modified net capacitance.