1. A method of building a monopulse calibration table from a live target of opportunity using signals received from the target at sum and difference antenna channels of a rotating radar antenna that receives signals within an angular-shaped beam, the center of which is the antenna's bore-sight, the angle formed between a reference direction and the bore-sight being an azimuth angle, the method comprising the steps of: a) at each of a plurality of N different azimuth angles, calculating a normalized received signal from a target of opportunity using a signal received from the target at a sum channel and using a signal received from the target at a difference channel; b) identifying the azimuth angle of where the target of opportunity is actually located as the azimuth angle whereat the magnitude of the normalized received signal obtained in step a) is greatest; c) for each of the other N azimuth angles of step a), calculating the difference between each of the N azimuth angles of step a) and the azimuth angle determined in step b) to obtain N, off-bore sight angles where each of the normalized received signals of step a) was determined; d) storing each of the normalized received signal obtained at step a) with a corresponding off bore sight azimuth angles determined in step c).