Don’t use your compass in a car
It was about 10 years back, and I was driving some boondock road in Central Oregon.
I was on a dirt road that seemed to be running directly north south, but I was feeling a bit turned around. So I stopped the car and got out my trusty Suunto M3 baseplate compass, to make sure I was driving in the intended direction.
Sitting behind the wheel, I pointed my compass straight ahead, spun the dial to put red in the shed and . . . The compass indicated that the road was heading pretty much east/west! Very puzzling!
Then I had an idea. I got out of the car, walked to the other side of the road, and once again took a bearing on the road in front of me. The compass now showed the road running exactly north south, just like I thought. Keeping a close eye on my compass needle, I walked back toward my car. When I got a few feet away, sure enough, the needle started slowly moving randomly. As I walked around the car with compass in hand, that large block of metal continued twitching my compass needle.
So, here’s The Takeaway. Don’t use a baseplate compass intended for backcountry navigation inside or nearby your car or any other large metal object. (Compasses that come built into the car, such is the one that might be on your rearview mirror, are already calibrated by the clever Car Engineering Gnomes to be correct.)
And, related to this, avoid using the hood of your car as a place to lay out your maps, take bearings, and in general do any kind of work with your compass. It’s usually is the largest, flattest and most convenient place to look at a map. But as you now know, trying to do anything that involves the magnetic needle of your compass on the hood of your car is a Bad Idea.
What are some other metal objects that can interfere with your compass?
electric power lines
belt buckles
zippers
most any sort of electronics, especially cell phones and avalanche transceivers
Try this: Put your mobile phone flat on the table, and move your compass slowly toward it, especially near the bottom (speaker part) of the phone. You should see the compass needle swing dramatically.
