The test of a mirror by the Ronchi method has shown to be very useful for testing concave aspherical mirrors. The analysis of a Ronchi pattern in order to find the experimental deviations of a given mirror whose theoretical shape is known, and the accuracy that can be obtained are described here.
A. Cornejo and D. Malacara, "Ronchi Test of Aspherical Surfaces, Analysis, and Accuracy," Appl. Opt. 9, 1897-1901 (1970)