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This chapter is from the book

This chapter is from the book

Set the Time and Date

See Also

Enable Automatic Time Synchronization (NTP)

Customize the Menu Bar Clock

Adjust the Format of Numbers and Other Notations

It's important for your Mac to be able to keep accurate track of the time. Lots of system functions depend on carefully scheduled execution; for instance, if you have Software Update set to check for new updates every week, or iSync set to synchronize your data every hour, your Mac must be able to kick off those processes at the correct time. These are just two of the functions you can see at the user level. As a Unix system, Mac OS X runs a number of self-cleaning and bookkeeping tasks every day—late at night, when you're most likely asleep, so that those tasks don't interfere with your work. You don't want to have the disk grinding away mysteriously at noon just because your system's time is set incorrectly.

If you don't have a network connection, you'll have to set the date and time for your computer manually. You use the Date & Time Preferences window to do this.

The time zone is an important part of your computer's time setting, especially when it comes to communicating with other computers around the world. If you send an email to someone on the other side of the country, for example, the email headers must be able to convey what time zone you're in, so that when the recipient gets the message, his email program can tell him when, by his clock, you wrote the message.

Apple provides a graphical method for choosing your time zone, and also allows you to select a nearby city to use its time zone information.

Figure 3.14Figure 3.14

  1. Open the Date & Time Preferences

  2. Open the System Preferences from the Apple menu. Alternatively, you can select Open Date & Time from the menu that appears when you click the time display at the far right of the system's menu bar.

    Click the Date & Time tab, if it isn't already selected. This brings up the manual configuration pane.


    The Network Time Protocol (NTP) allows your computer to keep its date and time in sync with a central server (see Enable Automatic Time Synchronization for more on NTP). If you don't have a network connection, however, you must check periodically to make sure that your Mac's time is accurate. Computers' clocks can drift over time, losing or gaining seconds or even minutes each week. NTP corrects this for you, but if you aren't networked, you must check the system time manually.

  3. Pick or Enter a Date

  4. Click a date in the graphical calendar to select another date within the current month.

    If the date you want is in another month, use the text field above the calendar to numerically specify a month. Click each of the date fields and either type a number or click a date field. You can increment the field using the Up and Down arrows.

  5. Move Clock Hands or Enter a Time

  6. On the graphical clock, click any of the clock hands and drag it to the position you want. Click the AM or PM display to toggle between them.

    If you prefer, you can enter the time manually. Click any of the time fields above the graphical clock and type a number or use the Up and Down arrows to increment the values.


    The analog clock remains in motion, with the second hand going around, until you start to make changes; if you move any of the hands, the second hand stops so that you can put it in an accurate position and apply it at exactly the right time by clicking Save.

  7. Click a Geographical Region or Select a City Name

  8. Click the Time Zone tab to bring up the time zone configuration pane.


    Don't worry about Daylight Savings Time or other such localized adjustment systems. If your calendar date is set properly, Mac OS X will know what the correct time zone mode is for whatever location you select. When your area "springs forward" or "falls back" for Daylight Savings Time, your Mac will automatically adjust the system time for you.

  9. On the graphical map, click as close to your geographical location as possible; the time zone for the location you click lights up. The map also shows the location of a city close to where you clicked (from which the system is actually deriving the time zone information).

    If you can't click your location on the map (for instance, if your time zone is really small), you can select a city in your time zone, and the system will adopt it. Use the Closest City drop-down menu to locate a nearby city; if you can't find a city in the list, it might be because the list shows cities only in the currently selected time zone. Select the text in the input box and begin typing the name of a major city in your region; the box auto-completes your input to show the nearest match, allowing you to type only as much of the city name as you have to before the system knows where you are.

    Press Return to accept a city name that has been automatically completed; your time zone will change to match that city.

  10. Save the Changes

  11. As soon as you make any changes, the Revert and Save buttons on the Date & Time pane become active. If you're not already on the Date & Time pane, click the Date & Time tab to open that pane. Click Revert if you don't want to keep your changes; click Save to apply the changes.


You are prompted to either Revert or Save your changes if you quit the System Preferences application or try to move to another preference pane before you click Save.

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