According to a recent estimate, there are about 40 types of calendars in use in the world today. Some calendars are regulated by watching the stars; others are carefully calculated based on scientific measurements. Calendars can be committed, by law, to written format; others are transmitted by oral tradition. Whichever calendar you follow, Microsoft Office Outlook 2007 is probably the number one choice for organising your business or social diary.

The history of how the Gregorian calendar evolved is complex. The Julian calendar, introduced by Julius Caesar in 45BCE (Before Common Era), was a solar calendar with months of fixed lengths. However, 45BCE is sometimes referred to by historians as the "year of confusion," because Caesar decided to insert 90 days to the Roman calendar to bring dates back to their traditional place in relation to the seasons. Caesar created a solar calendar with 12 months of fixed lengths and a provision for an intercalary (or leap year) day to be added every fourth year. As a result, the average length of the Julian calendar year was 365.25 days.

Following Caesar's death, the Roman authorities misapplied the leap-year rule, with the result that every third, rather than every fourth, year was a leap year. Although details are lacking, it is generally believed that Emperor Augustus corrected the situation by omitting intercalation from the Julian years 8BCE through 4CE. After this the Julian calendar finally began to function as planned. Caesar designated January 1 as the beginning of the year. However, other conventions flourished at different times and places. The most popular alternatives were March 1, March 25, and December 25. It served as a standard for European civilisation until the Gregorian Reform of 1582CE.

If you think that's confusing, spare a thought for those who aren't sure which calendar to follow. Even today, the use of the Gregorian calendar in the United States is only due to an Act of Parliament in the United Kingdom made in 1751, which specified use of the Gregorian calendar in England and its colonies. Its adoption in the United Kingdom and other countries was fraught with confusion, controversy, and even violence. It also had a deeper cultural impact through the disruption of traditional festivals and calendrical practices.

Thankfully, if you are using Microsoft Office Outlook 2007, you can be sure that things will run more to schedule and will be far less chaotic. And it's not only your calendar that can be kept in order. With Outlook 2007 you can view multiple calendars at once. These can be your calendars, shared calendars from other people, Internet Calendars, or Internet Calendar Subscriptions. You can open a second calendar in a new window and display up to 30 calendars in side-by-side view. You can also overlay calendars to see transparent calendars stacked on top of each other. This view is useful when you want to find a common free time slot on several different calendars.

In Calendar, the navigation pane shows a list of your calendars under 'My Calendars'. This list includes your default primary calendar in Outlook that displays your free/busy time to other people, and where meeting requests that you accepted are saved. Other calendars, or secondary calendars, can include calendars that you created to track a project, a personal schedule, or some other calendar event that you do not want to mix with the items on your default calendar.

For example, your default calendar might be your calendar for work, and your second calendar might track your new jogging schedule. When you share your default calendar, appointments on secondary calendars are not displayed to other people and do not affect your free/busy availability.

To open a calendar in a new window, in Calendar, in the 'Navigation Pane', right-click the name of another calendar that you want to view. Now click 'Open in New Window'. The calendar that you selected opens in a new Outlook window. To open a calendar in side-by-side view, in Calendar, in the Navigation Pane, select the check box of another calendar that you want to view. The calendar that you selected opens next to the calendar that is already displayed.

To overlay the calendars, in the Navigation Pane, select the check box of another calendar that you want to view. The calendar that you selected opens next to the calendar that is already displayed. Repeat these steps for each calendar that you want to view. On the 'Calendar' tab, click the left arrow. The calendars are now in overlay mode.

To add another calendar to the overlay, simply repeat these steps. At least one calendar must always be displayed. Or, to remove a calendar from the overlay stack, in 'Calendar', on the tab of the calendar that you want to remove from the overlay stack, click the arrow. The tab moves back to the right. The calendar that you selected is no longer displayed in overlay mode. Repeat this for each calendar that you want to remove from the stack. Again, remember that at least one calendar must always be displayed.

If you need to coordinate your business and social events accurately, don't do as the Romans did - put a date in your diary and find out how Outlook 2007 Calendars could help you stay in control.