The result of an electronic measurement of distance will only be affected very slightly by this curvature effect. Only in the case of long distances does it amount to more than the error which is in any case inherent in the process. This is probably the reason why little attention has been paid to it, and the errors due to curvature have been dealt with in different ways or even ignored. The IAG Special Study Group 19 for the electronic measurement of distance (1963) in Berkeley examined this problem for the first time since the questions of the velocity of propagation of waves and the adequacy of instruments were seriously taken up [10]. It will be of increasing significance in the future as the Maser and Laser enable greater distances to be measured.