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APPENDIX C 176 Differential Corrections Inc. Differential Corrections Inc. (DCI), of Cupertino, California, also provides DGPS services to its subscribers using a 57 KHz FM subcarrier. DCI utilizes radio data system (RDS) technology, also originally developed in Europe, that transmits data at 1187.5 bits per second. As of August, 1994, DCI had 46 FM stations operating in their DGPS network, with another 51 stations scheduled to begin service, effectively covering every major population area in the United States. DCI also operates in several foreign countries and hopes to expand their international service. The differential correction broadcast to DCI users is determined by reference stations located at each of the FM stations within the network. As with ACCUPOINTs service, the user equipment required to receive the FM subcarrier frequency resembles a typical pager. DCI provides its customers with three levels of accuracy at three different prices. The premium service has an advertised accuracy of 1 meter (2 drms), the intermediate service provides 5-meter accuracy, and the basic service gives a customer 10-meter accuracy.