AbstractThe contribution of refraction to the total error in electromagnetic distance measurement has become more prominent as the instrumental errors have decreased. Research with a high precision instrument, the Geodolite, has shown that changes in the refractive index tend to be the same on all lines measured from the same station at the same time.Ratiosformed from these measurements are more precise than the measured lengths. Knowledge of the daily variation of temperature in the lower atmosphere explains why temperatures observed for calculating the refraction correction are in error and why the ratio should be more accurate.When ratios are adopted as the observed quantities, the shape of triangles and more complicated figures can be calculated from newly-derived formulae and the figures can be adjusted using the method of conditions (correlates). The number of conditions turns out to be the same as in the adjustment of figures using angles, and the types are analogous.This new approach to the utilization of distance measurement eliminates many of the disadvantages of trilateration as compared with triangulation, and should facilitate the use of distance measurement, with all its attendant advantages, in control surveys.