Therefore, the "City Code" isn't a set of static rules. It is an . The city’s master clock must be linked to an astronomical calculation (usually the Islamic Society of North America (ISNA) or Umm al-Qura standard) that updates traffic signals, school start times, and waste collection schedules daily.
While button layouts differ by model, the general procedure for inputting a City Code is standardized across most Al Fajr units (such as the popular CJ and CT series): al fajr clock city code