Does your notebook calendar start on Sunday or Monday? In Japan, the notebook calendar starting on Sunday is commonly used, but the calendar starting on Monday is becoming increasingly popular due to the spread of a five-day workweek. On the contrary, in Europe, not only notebook calendar but also most of calendars start on Monday. Furthermore, the week number starting on Monday is also frequently used to determine the date of delivery, for example, 'delivery by 12th week Monday'. Meanwhile, the USA that does not follow the European standards such as the metric system is using unique week number system. When you use the week number in the business, you need to pay attention to the difference of week number system.