It is present practice to eliminate 'first order' refraction effects from TRANSIT doppler data by using the doppler shifts at two frequencies. If an effort is made to correct higher order refraction errors by using doppler shifts at three or four frequencies, the effect of errors other than those caused by refraction is increased. It is shown that these other errors must be decreased before higher order refraction correction is useful. It is further pointed out that the erratic errors which constitute a bar to further refraction correction are useful as a measure of other types of system error. Reduction of these erratic errors constitutes a simple criterion of improved system performance. (Author).