Citizen BT0001-63E Gents Eco-Drive Perpetual Calendar Watch. The unique feature of this watch is the large size date display in the center of the face. Thanks to the unconventional combination of two different size disks, the date is easily seen. Eco-Drive” solar powered generating system, meaning that there is no need to ever change batteries; 365 Days power reserve when fully charged. Perpetual Calendar. Insufficient Charge Warning Function. Overcharge Prevention Function. Approximate case diamter: 45mm. Stainless Steel Case and Bracelet. Eco-Drive movement. Black dial. Water Resistant 100 meters.