Low-level wind observations were made by manual theodolite readings of pilot balloon positions. Simultaneous readings were made from three theodolites with time intervals ranging from 5 to 60 sec. and for altitudes up to 8,428 ft. above the surface. The theodolite readings were analyzed as three simultaneous double theodolite observations of the wind vectors between the successively observed positions of the balloons. If the theodolite readings were completely accurate, each of the three simultaneous wind vectors would be identical. The differences between the magnitudes and directions of the horizontal components of the simultaneous wind vectors were used as a measure of the observational accuracy of the balloon movements. Twenty-sec. intervals between theodolite readings were found to give the greatest accuracy; the accuracy decreased rapidly as the time interval was shortened but the accuracy was nearly the same as the time interval was increased.