This model had a power transmitting roller made from rubber,
and the main unit of the lamp was molded from phenol resin. Through a durability test, it was determined that the rubber roller was likely to wear, and the molding part of the lamp unit was likely to crack. The engineers started development of an improved model by changing the materials for the roller and lamp unit to metal. Test equipment was installed in the factory garden, and durability tests were carried out all day and night.