| 摘要 |
In a position measuring receiver, when ephemeris data is acquired from radio waves received from satellites in the measurement of a present position of the receiver, the acquired ephemeris data and data on a time when the ephemeris data was acquired are stored (steps SA6-SA8). Then, a time elapsed since the ephemeris data was acquired is calculated at intervals of one minute (steps SA10-SA12). After the elapsed time is more than two hours, an alarm is sounded at intervals of two minutes (steps SA13-SA14) to urge a user to acquire new ephemeris data at a spot suitable for receiving radio waves from the satellites before an effective term of the old ephemeris data is expired.
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