Comparison of contemporaneous measurements of 84 distances in the range of 10 to 50 km by both Global Positioning System (GPS) and Geodolite (an electro-optical distance-measuring instrument) indicates that the Geodolite measurements are systematically longer by 0.283¿0.100 parts per million of the measured distance. Quoted uncertainty is 1 standard deviation. This amounts to 11.3¿4.0 mm at 40 km, which is near the maximum Geodolite range. The systematic difference is within the random uncertainty of an individual GPS-Geodolite comparison and was detected only from an analysis of a large number (84) of such comparisons. The source of the systematic difference has not been identified.