| 摘要 |
There are included a movable body on which an ultrasonic wave signal output part for producing and outputting an ultrasonic wave signal of a particular frequency is mounted; an ultrasonic wave signal reception part for receiving the outputted ultrasonic wave signal; a determination part for determining the difference between the frequency of the ultrasonic wave signal received by the ultrasonic wave signal reception part and the particular frequency; a calculation part for calculating the speed of the movable body from a signal of the determination difference; and a display part for displaying a result of the calculation.
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