Disclosed is a grand master clock. The grand master clock comprises: a GNSS interface receiving GNSS time synchronization data; a real-time clock including a crystal oscillator; one or more communication interfaces exchanging data with clock correction sources; and a clock correction host. The clock correction host calculates clock drift based on the GNSS time synchronization data and data from the clock correction sources, generates adjusted clock data, and writes clock data adjusted by the real-time clock from different positions. The grand master clock may be in a vehicle. According to the present invention, power use of the autonomous vehicle may be reduced.
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