Along with other factors, accurate radar target location is dependent upon a knowledge of the electromagnetic propagation path. The propagation path is a function of the characteristics of the medium through which the signal travels. Advances in the resolution capabilities of modern electronic tracking equipment have led to requirements for more accurate prediction of atmospheric refraction characteristics. The inherent error of the equipment is, in many cases, less than the error introduced by the atmospheric refractive effects. After corrections to observed launch angle and target range have been made on the basis of atmospheric refraction information, residual errors in range and angle determination may exceed the instrumental error of the radar. The value of designing a system, perhaps at considerable expense, to provide accuracies better than the limits presently imposed by these residual errors is questionable