For improving the drawback of brightness decay of a display due to aging, a memory can be used to store the usage time of each pixel of the display, then based upon the usage time the brightness decay of each pixel of the display can be compensated and accordingly the value for the compensation can be stored in a volatile memory and a non-volatile memory. However, the usage of the non-volatile memory is limited. Hence, the present invention discloses a new approach for storing the data so as to decrease write-in sequence per unit area for the non-volatile memory rather than increasing its storing capacity proportionally.