Patent ID: 8316067

Claim:
An arithmetic control unit comprising: an operation digit number input section which inputs a number of operation digits according to a user operation; an operation type designating section which designates a type of an operation according to the user operation; a first operation executing section which executes an operation of the type designated by the operation type designating section in the number of operation digits input by the operation digit number input section; a second operation executing section which re-executes the operation in an added number of operation digits which is the number of operation digits input by the operation digit number input section with a predetermined additional number of digits added thereto; a value comparing and underflow digit number detecting section which compares values of individual digits of a result of the operation re-executed by the second operation executing section with values of individual digits of a result of the operation executed by the first operation executing section, and detects a number of digits which do not have a value match as a number of underflowed digits; and a display control section which performs display control to display the number of underflowed digits detected by the value comparing and underflow digit number detecting section together with the result of the operation executed by the first operation executing section.