PROBLEM TO BE SOLVED: To easily check fish movements and fish types.SOLUTION: A server records measurement data and time information of each sonar and transmits the measurement data and the time information of each sonar to a terminal in response to a request from the terminal. The terminal, which is connected to the server via a network, comprises a display, operation input means, a display range determination part, a data request part, and an image data creation part. The display comprises prescribed areas No.1 to No.N (N is an integer greater than or equal to 2) which display measurement data. The operation input means receives an input for determining measurement data to be displayed. The display range determination part determines necessary measurement data to be displayed in response to the input received by the operation input means. The data request part instructs the server to send missing measurement data. The image data creation part creates image data to be displayed on the prescribed areas No.1 to No.N by using the received measurement data and the time information.
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