Abstract: PURPOSE:To prevent the malfunctioning with an easy handling by arranging one display to cocurrently perform a monitoring function of various data and a messaging function to users. CONSTITUTION:Previous information memorized in a mangetic card is read in with a card reader writer 3 and compared in computation with current information amplified with an amplifier entered from a sensor by means of an arithmetic processor and the comparison results are indicated on a display. A display 4 indicates the operation procedure corresponding to an operation button depressed prior to the execution of the computation and the contents in execution during the execution thereof. The display 4 indicates various data involved in the multimeter mode or in the data checking mode with the depression of a multimeter switch 8 or a data checking switch 10.