Long-distance measurements (10 m - 1000 m) with an accuracy of 10-7 is achievable with Frequency Shifted Feedback (FSF) laser interferometry technique, provided that the determination of the radio frequency beat order be made without ambiguity and on a time scale compatible with atmospheric applications. Using the pulsed-FSF laser that we developed for laser guide star application, we propose and test a simple method for measuring the beat order in real time. The moving-comb and Yatsenko models are also discussed. The first of these models fails to interpret our long-distance interferometry results. We show that the accuracy of long-distance measurements depends primarily on the stabilization of the acoustic frequency of the modulator.