The observations from all receivers are downloaded to the computer for processing. Single differences are the differences between the carrier-phase observations of two receivers of the same satellite at the same epoch. These differences essentially are free of satellite clock errors. Next, the double differences are formed. Double differences are the differences of two single differences of the same epoch that refer to two different satellites.
Double differences are largely independent of receiver clock errors.
Synchronization of the receivers to 0.1 microseconds is sufficient, in that the remaining clock errors do not affect the double differences beyond the measurement accuracy of, for example, 0.01 cycles. Thus, differencing is an effective compensating technique for our inability to realize perfect time synchronization. The differencing scheme can be continued. For example, one can compute the difference of two double differences of two different epochs. One novelty of the triple difference is that it does not depend on the initial integer ambiguity, because this unknown is a constant in time.