April 27, 2004

By Karen Kenworthy


I wonder. A few days ago we switched to "Daylight Saving Time" here at the secluded Power Tools workshop. Now that our clocks have been reset, we have an extra hour of glorious daylight each evening.

But are we really enjoying saved daylight? Perhaps squirreled away last winter when our clocks were running on Standard Time?

Or is this extra daylight actually borrowed? After all, this is a government program. I suspect we're really squandering some of the coming winter's precious warmth and light, instead of dipping into our empty sunshine stores.

Sure, the extra hours feel great now. More time to sit on the porch. More time to work in the garden after supper. But a few months from now, when the bill comes due, when we're shivering in the dark, we may regret this little horological accounting trick ...

Times, They Are A 'Changin

All the recent talk about clocks and time got me thinking how our computers measure and manage time. I'm sure you know that deep inside each computer is a "real-time clock", or RTC. This circuit works a lot like the little clock on my nightstand. Set it once, and ever after it reports the correct time of day.

Your computer's clock has one bonus feature not found on many household clocks. In addition to reporting the current time, it also reveals the current date. That's why these little gadgets are sometimes called "clock- calendars".

To handle these two jobs, computer clocks must know the relationships between seconds, minutes and hours, and days, months and years. They must also understand leap years, automatically adding an extra day to February when required. All in all, they're pretty impressive bits of silicon.

But as bright as these electronic time keepers may be, they have some limitations. For example, our computer clocks don't know about time zones. To them, time is the same everywhere around the world. Move a computer half-way around the world, and its clock will still show the time in the land from whence it came.

Computer clock-calendars are also unaware of Daylight Saving Time. Come winter, spring, summer or fall, they blithely tick away. Every twenty four hours brings one new day. Their clock steadily advances, never springing forward or falling back, never lengthening or shortening any day.

Fortunately, Windows works around these shortcomings. Unlike our computer clocks, Windows knows a lot about time zones. In fact, it comes with a built-in list of more than 70 of the world's time zones.

When first installed, Windows asks us to select one of these. Later, this choice can be changed by running the Date and Time applet found in Windows' Control Panel. You can also select a new time zone by double- clicking the time displayed in the lower-right corner of the Windows desktop.

Time Zones

So, what exactly is a time zone, anyway? To you and me, it's a geographical area, a region of the earth. Everywhere within that area, the local date and time are the same.

For example, my baby brother Kevin lives near Washington, D.C., along the eastern coast of the United States. When it comes to time zones, this portion of the world is known as "Eastern Time (US and Canada)".

As hard as it is to believe, almost all the millions of clocks, watches and computers found in this zone are in agreement. Thanks to this synchronization, Kevin and his co-workers arrive at work, and break for lunch, in unison. And Senators and Representatives can simultaneously depart for well-earned weekend vacations after three hard days of television interviews and other grueling duties.

The story of time zones starts in a little town called Greenwich, nestled along the river Thames in southern England. Since 1675 it has been the home of the Royal Observatory, founded in large part to make measurements that improve the quality of naval charts and other maps.

Now, being mathematicians at heart, navigators longed for a geometric "coordinate system" to specify locations across the globe. But the earth isn't flat like the graph paper we nerdy kids used in High School. Instead, it's a sphere, round like the basketballs the other kids studied.

You know the rest of the story. Mapmakers settled on lines, called "latitude" that run east and west, circling the earth's poles at varying distances. Another group of lines, called "longitude", run north and south, passing through the earth's poles.

To complete the picture, we simply needed a standard way to number these intersecting lines. For that we need a starting point ...

Picking the primary, or first, line of latitude was easy. The Equator is the longest such line. Thanks to that, and its central location, it was chosen. All other latitudes are known by their distance (in degrees North or South) from there.

But there's no obvious choice for the first line of longitude. That is, unless you happen to work at the Royal Observatory, or depend on their tables of observations. In that case, the natural primary line of longitude is the one passing directly through the cross-hairs of the eyepiece of the observatory's "Transit Circle" telescope.

This choice seemed so logical, to so many, that in 1884 the "International Meridian Conference" made this custom a world-wide standard. Greenwich became the official home of the "Prime Meridian", the starting point for all east-west measurements. Now, every line of longitude is known by its distance (in degrees East or West) from Greenwich.

The same conference that created the Prime Meridian also defeated a proposal to create twenty four standard time zones. Instead, individual countries, and sometimes even states and cities, have been left to define local time. As a result, we now have a quirky quilt of irregularly shaped time zones, each with their own definition of local time.

But these time zones have a few things in common. For example, the year- round average solar time along the Prime Meridian is used as the starting point by all time zones. Each zone's local time is specified as a number of hours and minutes ahead of, or behind, this "Greenwich Mean Time" (GMT).

Kevin's Eastern Time zone is currently 5 hours behind GMT. So, when it's 6 p.m. in Greenwich, it's only 1 p.m. in Washington, D.C. Using a common shorthand, Kevin's zone is "GMT-5:00", or GMT minus 5 hours and zero minutes.

The zone containing the city of Amsterdam is "GMT+1:00". So, when it's 6 p.m. in Greenwich, local time in The Netherlands is already 7 p.m. Oddly, the Central Australia Time zone is currently GMT+9:30, or nine hours and 30 minutes ahead of GMT. As a result, at 6 p.m. in Greenwich, it's 3:30 a.m., the next morning, in Adelaide!

The difference between local time and Greenwich Mean Time is known as the time zone's "bias" or "offset". All time zones have at least one bias. But many have two.

One offset, called the Standard Time bias, takes effect during the winter months in the Northern Hemisphere, and during the summer down under. The other offset, called the Daylight Saving Time (DST) bias, takes over during the summer up north, and in the winter where folks live heels over heads.

Besides a second bias, time zones where Daylight Saving Time is observed have two special dates: One when DST begins, the other when it ends. Usually this date is specified indirectly. For example, in the United States, Daylight Saving Time begins the first Sunday of April, at 2 a.m. Daylight Saving Time ends on the last Sunday in October, also at the delightful hour of 2 a.m.

But other zones follow other rules. In Adelaide, Australia, Daylight Saving Time begins the last Sunday in October, and ends the last Sunday in the following March. Helsinki changes their clocks at 3 a.m. on the last Sundays of March and October. And in Korea, Daylight Saving Time is never observed.

Karen's New Zone Manager!

Windows does a pretty good job of managing this crazy collection of time zones. But its built-in list isn't perfect. For example, some readers tell me they find themselves in parts of the world where Daylight Saving Time isn't officially recognized, but is observed by their employer.

That's one reason I've written the latest Power Tool, called Karen's Zone Manager. It allows you to supplement Windows' time zones some custom zones of your devising. When creating a new time zone, you're in charge. You choose the zone's Standard and Daylight Time bias. The dates Daylight Saving Time starts and stops, or whether DST is observed at all, are entirely up to you too.

After you've used my new program to create a custom time zone, you can use the new zone just like one of Windows' own. It will appear in Windows' list of time zones, just like those Windows was born with.

But the new Zone Manager to change your computer's current time zone too. Just select one of your custom zones, or one of Windows' built-in zones, from it's on-screen list. Then click the program's big "Activate Zone" button.

Better yet, use the Zone Manager to create desktop shortcuts to your favorite time zones! Then you can switch time zones with just a double- click of your mouse. It almost makes traveling from zone to zone fun. :)

When switching zones, the Zone Manager also adjusts your computer's clock ensuring it always shows the correct local time in every zone. It can also contact one of the Internet's ultra-precise "Time Servers", synchronize your clock to theirs, giving your computer the correct time within a few thousandths of a second!

The program includes a list of dozens of public time servers, one of which is probably nearby. But the Zone Manager can make use of any time server that supports the popular "Network Time Protocol" (NTP) Internet standard. The program adjusts the Greenwich Mean Time, the server reports, to the local time you need.

There's a lot more to say about time and the new Zone Manager. But it's getting late. We'll have to wait until another day. In the meantime, I hope you'll give the new Zone Manager a try.

As always, the program is free for personal/home use. To download your copy, visit the program's home page at:


If you're a programmer, download a copy of program's Visual Basic source code too! It has some cool new "classes" for managing information about time zones you might enjoy.

Better yet, get the latest version of every Power Tool -- including the new Zone Manager -- on a brand-new, shiny CD. You'll get three bonus Power Tools, not available anywhere else, too. Source code of every Power Tool, the text of every issue of my newsletter, and some of my original Windows Magazine articles, are included. And owning the CD grants you a special license to use all my Power Tools at work.

Best of all, buying a CD is the easiest way to support the KarenWare.com web site, Karen's Power Tools, and this newsletter! To find out more, visit:


Until we meet again, be enjoying our extra daylight. And if you see me in the garden, in the shade, or on the 'net, be sure to wave and say "Hi!"

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