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The authors present a quasi-interferometric technique for measuring the flight times of signals broadcast by global system for mobile communication (GSM) transmitters, together with measurements made using the technique in and around Cambridge, UK. The data are used to determine the errors associated with GSM signal arrival times in various environments. The majority of the timing errors in all signal environments lie in the range -1 to +1.5 μs, with the tails of the distributions extending beyond +3 μs. The authors show that these large timing errors are caused by the distortions of the cross-correlation peaks used to determine the signal arrival times as a result of coherent multipath interference. Models of timing errors, based on Cauchian distributions, fit the experimental data better than those based on symmetrical or skewed Gaussian functions. This has implications for attempts to combine GSM and global navigation satellite system measurements using Kalman filters.