Calculating machine comprising a microprocessor (1) controlling the operations carried out by the machine, a stack (2) of shift registers connected to the microprocessor and intended for the temporary storage of the numbers with which the operations are to be carried out, a read only memory (ROM) (7) containing the programs relating to the functions of the machine, a display controller (5) connected to the microprocessor (1) and to the ROM (7) and a screen (10) for displaying results, characterized in that it furthermore has means for displaying on the display screen (10) of the machine educational information relating to the mathematical rules governing the operation carried out by the machine.

A portable electronic computer for conducting fraction calculations has a display including a first multiple-digit display area for displaying the numerator of a fraction, and a second multiple-digit display area for displaying the denominator of the fraction. The numbers of digits of the numerator and denominator of a fraction to be displayed are obtained. The number of digits of the numerator is compared with the number of digits of the denominator. The difference between the number of digits of the numerator and the number of digits of the denominator is calculated. When the number of digits of the numerator is smaller than the number of digits of the denominator, the numerator is displayed on the first display area with its position shifted to an upper digit place according to the difference. When the number of digits of the denominator is smaller than the number of digits of the numerator, the denominator is displayed on the second display area with its position shifted to an upper digit place according to the difference.

In a calculating device, a method to allow a user to enter fractions in the form "b/c", where "b" and "c" are integers; "b/c" is a fraction; and the denominator "c" is within a prespecified range. The method to enter real number fractions includes activating one or more digit keys and the successive pressing of a primary function key to distinguish the previously entered numerator value from a subsequently entered denominator value.

The specification discloses a woodworking and home improvement calculator particularly adopted for symplifying common home improvement calculations. The calculator includes a variety of special keys including a gravel, cement, tile, brick, block, 4.times.8 sheet, paint, wallpaper, stud and roof bundle keys which allow the user to quickly determine the amount of materials needed for projects involving the aforementioned keys.

Method for automatically adding scale symbol to operation formula during operation and system for executing the method. The system includes: an input unit for keying in operands and choosing the scale thereof; an input/output buffering unit for temporarily storing the input data; a synchronously checking unit for checking the whether the input operands conform with the scale; a scale symbol adding unit for reading and automatically providing the symbol of the scale and sending the symbol to the input/output buffering unit and a mathematic logic calculating unit to be operated and wait for further instruction. After operated, the data are displayed by an output unit or stored in a memory. The data can be stored in both a read-only memory for check in next use or temporarily stored in a dynamic random access memory for checking the data source of the result and the scale.