1. An apparatus for analyzing the characteristics of a periodic structure formed on a sample comprising: a spectroscopic measurement system including a broad band probe beam directed to reflect off the periodic structure and a detection module for measuring either the change in magnitude or phase of the probe beam at a plurality of wavelengths and generating output signals corresponding thereto; and a processor system including a master processor and a plurality of individual slave processors arranged to process data in parallel, said processor system using the output signals generated by the measurement system to characterize the periodic structure on a real time basis, said processor system using an algorithm which includes a model of the periodic structure and which calculates a set of theoretical data at each of a plurality of wavelengths based on an initial assumption of the characteristics of the periodic structure and compares the theoretical data to normalized data derived from the output signals and thereafter modifies the assumption of the characteristics of the sample based on the results of the comparison and recalculates a new set of theoretical data, with the comparison and recalculation steps being repeated until the differences between the calculated data and the normalized data are minimized and wherein the calculation of theoretical data is distributed by the master processor to the slave processors and wherein each slave processors performs calculations at selected wavelengths in parallel so that time needed to reach the desired result is minimized.