PURPOSE:To enlarge and display part of a graph display by retrieving a storage part according to a numeral converted to compare a coordinate position in a graph with actual data and extracting corresponding coordinates. CONSTITUTION:A cursor mark '+' which can be moved to an optional point in the graph associatively with a mouse is moved and the numeral obtained by a mouse coordinate-numeral conversion part 7 by the reverse arithmetic of calculation performed by a trend coordinate arithmetic part 2 from coordinates A in the graph obtained by the clicking of the mouse is denoted as A'. The mouse is clicked to obtain a point B on the opposite side from a part A to be enlarged and displayed. An in-storage-part retrieval part 6 extract the coordinates of the part to be enlarged and displayed from data in the storage part 1 by using coordinates B' calculated from the above coordinates and calculated by a trend coordinate calculation part 2, and the result is stored in a frame memory 3 and displayed on a display part 5 through a video generation part 4.
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