The International GNSS Service (IGS) clock products contain clock information about the local reference for the IGS tracking receivers with respect to the IGS time. The clock information is obtained from GPS carrier-phase measurements. Many timing laboratories now operate IGS tracking receivers using high-quality clocks as the local reference. The IGS clock products allow timing laboratories to use the GPS carrier-phase measurements for comparing these clocks without significant postprocessing by the user. In this paper, we study the stability of remote clock comparisons performed with the IGS clock products during the past 2 years. We compare the remote clock differences obtained with the IGS clock products to the remote clock comparisons with two-way satellite time and frequency transfer and GPS common view. We focus on the long-term differential performance of these transfer systems, on the order of many months.
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