An image forming apparatus increases a primary-transfer pressure contact force at the times of primarily transferring black color to a first sheet and yellow and black colors to a second sheet or subsequent sheets in order to prevent misalignment of colors. Data is stored in memory cells of the first cell strings, and the second cell strings are configured as a data non-storage region. On the upper surface of the upper ball receptor is located an embellishment element consisting of at least one LED that is illuminated by a source of electrical power supplied by a vehicle electrical circuit. In embodiments, potential boundary vertices arrays may be employed to store potential boundary vertices for a next iteration, for vertices being visited in a current iteration.