The Datum 9390 GPS Timing Unit operates on the civilian l-band (1575.42 MHz) utilizing C/A (Coarse Acquisition) code transmissions to monitor time and frequency data from the Navstar satellite constellation. The 9390 Time and Frequency are determined from satellite transmissions and calculations referenced to United States Naval Observatory through the GPS master Clock System. This link provides Traceability to USNO and all international time scales.