How to keep your Mac’s clock accurate
Mac Tip #422, 03 February 2010

Do the clocks round your house or office gradually gain or lose time? It’s annoying. Your Mac’s clock could ‘drift’ too. Here’s how to make sure it’s always correct.

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Timestamped files.

Timestamps

As you work and play on your Mac the clock is keeping track of the date and time in the background.

If you create a new file, or save one, or save changes to a file, your Mac adds a timestamp: a record of when the action took place.

The timestamp is often used by the system to decide which version of a file is ‘current’ or ‘more recent’.

The clock on your Mac is also used to display calendar reminders, timestamp emails, carry out regular activities, such as to check mail every 10 minutes between 8 am and 6 pm — anything that has some type of ‘time’ connection.

Time Zones.

Time travel

As you’ll know if you’ve ever travelled with a laptop, ‘time’ is a fairly fluid thing. When it’s 6 pm in one part of the world it is 2 am in another.

When you travel with a laptop you need to be able to change the Mac’s clock to reflect the local time.

Date & Time System Preference

The important System Preference to visit is Date & Time.

Clock

The Clock tab allows you to set display options for the Clock in the Menu Bar and for announcing the time.

Time Zone

The most important tab is the Time Zone tab. Click on the map to choose a general location, and then choose your closest city from the drop-down menu.

This tells your Mac exactly where you are.

The relevant timezone is highlighted on the map, and your Mac’s clock may change if it was previously set to another location.

If you travel with your Mac, adjust the timezone and closest city when you arrive at a new destination.

Set the time automatically

If you’re using Snow Leopard you will notice a checkbox near the top of the Time Zone tab beside the words Set time zone automatically using current location. In my experiments it failed to discover my location. It’s worth a try for you.

This setting uses information about WiFi networks near you to work out your location.

When I tested it, I was at home. It’s unlikely any service knows the location of my home wireless network, but public WIFi network information may allow your Mac to be located.

Date & Time

The Date & Time tab of the Date & Time System Preference has a crucially important setting: the Set date and time automatically dropdown menu.

Provided you have a regular connection to the Internet check that box, and then choose a Timeserver from the drop-down menu.

A timeserver is a computer that always knows the correct time, based on an extremely accurate master clock.

It doesn’t really matter which timeserver you choose, but you may like to pick the one closest to where you are.

Your Mac regularly connects to the timeserver, discovers the correct time, and adjusts its own clock to match. No more being behind (or ahead) of the times!

Share your experiences with Date and Time below.