To instantaneously select a calculation method to be used in the case of calculating plural input items in a table displayed on a screen.
When data are inputted to one of the input item areas 11 and 12 of a display item area 1, whether or not the input data are proper is checked and the code is set to input state areas 21 and 22. A value obtained by the calculation method 1 is displayed in a calculated result area 13 in the case that the codes of the input state areas 21 and 22 are both proper, the value obtained by the calculation method 2 is displayed in the calculated result area 13 in the case that the input state area 21 is proper and the input state area 22 is improper, the value obtained by the calculation method 3 is displayed in the calculated result area 13 in the case that the input state area 21 is improper and the input state area 22 is proper and it is defined that calculation is impossible and a blank is displayed in the calculated result area 13 in the case that the codes of the input state areas 21 and 22 are both improper.
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