- Old world inspiration meets new world technology in this retrograde perpetual calendar with alarm unlike any other. Citizen Eco-Drive's iconic stainless steel watch with blue features dual time, month-day-date, 12/24 hour time, non-reflective crystal, a 39mm screw-back case, 100M WR and foldover clasp with hidden double push button. Featuring our Eco-Drive technology – powered by light, any light. Never needs a battery. Caliber number E870.