Accuracies Angles can be measured to about 1 arc second(5×106 radians) EDM measures distances to 1X10-(1 part-per-million, ppm) Atmospheric refraction 300 ppm Atmospheric bending can be 60(more effect on vertical angles) 02/11/02 12.540Lec0202/11/02 12.540 Lec 02 9 Accuracies • Angles can be measured to about 1 arc second (5x10-6 radians) • EDM measures distances to 1x10-6 (1 part-per-million, ppm) • Atmospheric refraction 300 ppm • Atmospheric bending can be 60” (more effect on vertical angles)