Monday, February 6, 2023

Comparing Compasses

Not actually Erin.
& is used with permission.

Over my years as a prepper (and before that, as a Scout) I've accumulated a number of compasses. Some have been good, while others were clearly cheap trash. However, many of them occupy the realm of "I'm not sure."

It's easy to tell if a compass is broken, because they very clearly don't point toward north, or spin slowly, or otherwise have obvious errors. But how do you know if a compass is just slightly wrong?

I don't know if there's an official way to do it, but here's how I do it. 
  1. In a place without metallic or magnetic interference, determine magnetic north. You can do this with a known good compass or with a compass app on your smartphone. 
  2. Indicate magnetic north with a pencil and ruler on a clean sheet of paper. If you are using an app, place the phone on the paper and the ruler alongside the phone. 
  3. Place the suspect compass(es) on the paper and draw a line with the ruler and pencil along the azimuth the compass says is north. 
  4. Label each line. 
  5. Use the ruler to determine if the lines are parallel or not. 
Here's an example of this in action. The UST Compass is my Known Good. 

As you can see from this picture, the white ring compass (which arrived in an Apocabox) is parallel to my Known Good UST, whereas the black ring compass (which I found in my father's room) is mostly accurate, but there's some deviation to the west. 

From looking at this picture, could you tell that the top compass isn't accurate?

The other compasses my father owned were even worse. The brass compass deviates further west than the black ring, and the cheap Coughlan's compasses with LED lights are so wrong as to be completely useless. Those last three were thrown into the trash before I thought to write this article, so I have no pictures of them except through Amazon links -- and don't buy them for navigational purposes, please!

So that's how I determine if a compass is good or not. How do you do it?

No comments:

Post a Comment

The Fine Print

This work is licensed under a Creative Commons Attribution- Noncommercial- No Derivative Works 3.0 License.

Creative Commons License

Erin Palette is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to