Calculator capable of recovering cleared values

A calculator capable of recovering cleared values, comprising:

• an input unit including deletion keys for clearing currently displayed data or recorded data of the calculator, and an UNDO key for recovering the cleared data;
• an output unit for displaying status of the calculator and operating results;
• an input/output buffer coupled to the input unit and the output unit and providing a display buffer for temporarily storing input and output data;
• a memory for storing program codes and memory space required for operating;
• an algebra logic processor coupled to the input/output buffer and the memory for providing arithmetic and logical operations;
• a stack register coupled to the algebra logic processor for temporarily storing previously cleared data by one of the deletion keys, wherein whenever the displayed data or the recorded data is cleared by pressing one of the deletion keys, the cleared data is pushed into the stack register;
• and
• a flag register coupled to the algebra logic processor, and being set when the displayed data or recorded data is cleared by pressing one of the deletion keys, whereby, when the UNDO key is pressed and if the flag register indicates that the displayed data or recorded data was cleared by one of the deletion keys previously, a data entry is popped from the stack register and the flag register is cleared.