For example only the first day of the week, or all days of the week. You can choose between two different week number schemas: • Weeks starts on Monday: This is the standardized version (DIN 1355 / ISO 8601) and is used for example in Europe. • Weeks starts on Sunday: This is used in the USA, Canada, Australia and New Zealand. If you sync your iPhone calendar with iCloud, MS Exchange or with your Mac or PC, the calendar week numbers will also be synced. Enjoy this great and helpful App