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Old 02 Mar 2012, 01:33 am
Obsessed Cruiser
Join Date: Nov 2007
Location: Mooresville, NC
Posts: 5,324

I'm posting this here as I've heard over the last three weeks of four owner's having CAL indications on their EVIC. Only seen one here, but have bumped into others on other forums. So for your benefit, I wanted to post this to help you out in calibrating the compass in your PT Cruiser.

Note that annually you should calibrate your compass. When you calibrate it, what you're actually doing is correcting your compass for "magnetic declination". What that does is correct your compass for the differences between 'true north' and 'magnetic north'. If you are interested in reading up on the effects of magnetic declination you can find it on Wikipedia.

Magnetic north moves every year. This is why I suggest you calibrate your compass once per year. Here is a graphic that gives you a simple indication of how declination changes over time:
What you see scrolling across the top are the dates, from 1590 to 1990.

Here's an interesting comment from one of the Live Science authors, from January 7, 2011:
Originally Posted by Wynne Parry
Earth’s Magnetic Field Shifts, Forcing Airport Runway Change

The magnetic north pole is currently hovering over the North Sea and moving toward Siberia. This means two Florida airports are renumbering their runways. Odd as this connection may appear on the surface, the adjustments under way at Tampa International Airport and beginning next week at Peter O'Knight Airport are the result of a natural, ongoing process.

Earth's magnets

The Earth has an iron core, and movement within its outer part is likely responsible for sustaining a magnetic field, which constitutes much of what we measure at the Earth's surface. As a result, the Earth resembles something of a giant magnet with two poles: magnetic north and magnetic south. However, its field is not perfectly symmetrical and has undulations that are always moving around, according to Jeffrey Love, a research scientist with the U.S. Geological Survey's Geomagnetism Program.

The magnetic poles don't line up with the geographic ones, and the difference between them is an angle called declination. As if this wasn't enough of a nuisance for navigators, the Earth's magnetic field drifts, causing the angle of declination to change over time. In fact, it drifts about one-fifth of a degree a year at lower latitudes, such as Florida. "So that means if you wait five years, the compass will be off by one degree," Love said. For long-distance air travel, an error of only a couple of degrees could translate to arriving in the wrong airport, Love said.

Declination also varies depending on location. At high latitudes, it tends to become larger, and a compass becomes increasingly unreliable. If you were to stand over a magnetic pole, and tried to use your compass, it would not know where to point, Love said. Longitude also factors in. As the patterns of motion of the molten iron in the Earth's core changes, so does the shape of the magnetic field, he said. Right now, the magnetic north pole, where the field is vertical, is located at 84.97 degrees North and 132.35 degrees West, above the Arctic Ocean and drifting generally north-northwest toward Siberia at about 55 kilometers (34.2 miles) per year, according to Love.

What's going on in Florida?

Travelers have struggled with the complexity of navigating by compass for centuries, and modern American travelers are no exception. Runways are designated according to the points on a compass, and the drifting magnetic north means that they, periodically, need to be renamed. "Recently, the drift has caused our runways' orientations to be closer to the next increment on the magnetic compass," Tampa International Airport spokeswoman Brenda Geoghagan told LiveScience in an e-mail.

For example, the west parallel runway, which was named 36Left —18Right to designate compass points of 360 degrees and 180 degrees, is being renamed to 1Left — 19Right, to indicate 10 degrees and 190 degrees, since the runway designations are separated into 10-degree increments.

Adjustments to runways like this and to navigational aids are ongoing, according to Kathleen Bergen, a spokeswoman for the Federal Aviation Administration's Southern Region. A third airport is scheduled to rename its runways in October; however, the changes aren't necessary for all airports in the Tampa Bay area, she said.

Every five years, federal agencies tabulate and publish a value called magnetic variation, which varies by location. Similar to declination, it correlates true direction to the magnetic compass readings needed for navigation.

These values are used to update navigational aids, such as instrument landing systems and beacons, she said. If there is a change of more than three degrees at any given airport, then runways need to be renumbered, as is happening at the Florida airports, Bergen said.

While aviation in the United States still relies on ground-based radar, which is calibrated to the local magnetic variation, it is moving toward a satellite-based system. "Runways are still aligned toward magnetic poles. That’s not going to change," she said.

A Much Bigger Change?

The same forces that cause the magnetic poles to drift can also cause a more dramatic change by switching the magnetic north pole to magnetic south pole, and vice versa, Love said. In fact, the physics behind the activity in the Earth's core could just as easily generate a polarity opposite of what exists today, he said. The poles last reversed themselves 780,000 years ago, and the reversals typically take 10,000 years or more to happen.

"In terms of what kind of havoc it could wreak or effects on humankind, we can't really say because we haven't experienced it," he said. "I don't think it will be the end of the world."
Add to this, about mid-year 2011 we had a huge shift in the magnetic fields. So what you do to calibrate your compass is add in the zone you live in, then run the calibration loop. This allows your compass to focus on the variation needed to make up for changes in declination.

Your owner's manuals have an entire section dedicated to this. In chapter 4 of the '06 and up manuals you can find information on page 236 regarding the zones for calibrating your compass properly. On page 238 of the '06 owner's manual you'll see the following:

Originally Posted by '06 Owner's Manual Page 238
The Cal indicator will come on continuously in the EVIC display to indicate that the compass is now in the calibration mode and that the vehicle can now be driven to calibrate. (A short EVIC button press from the Calibrate Compass (Yes) screen will exit the EVIC Customer Programmable features, and return it to its normal operating mode). To complete the compass calibration, drive the vehicle in one or more complete 360 degree circles under 5 mph (8 km/h) in an area free from power lines, large metallic objects, until the CAL indicator turns off. The compass will now function normally.
Note that sometimes it looks like CRL instead of CAL!

If you don't have an owner's manual, go to the thread I posted in the Tech/Performance section and download a copy in PDF.

Last edited by Chromenut; 02 Mar 2012 at 01:35 am.
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Old 02 Mar 2012, 03:38 pm
UptownSport's Avatar
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Army map reading, you always (unless it was 0 degrees declination) had to account for magnetic declination.
It was printed on our maps, and depending on the area sometimes quite substantial
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Old 02 Mar 2012, 04:32 pm
Obsessed Cruiser
Join Date: Nov 2007
Location: Mooresville, NC
Posts: 5,324

Originally Posted by UptownSport View Post
Army map reading, you always (unless it was 0 degrees declination) had to account for magnetic declination.
It was printed on our maps, and depending on the area sometimes quite substantial
Same same for the Air Force. Man on mountaintops you really had to work to get the declination correct!
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