Discussion: Does my compass point north?

I just got back from NEOC A meet to discover that it seems like my moscow compass may no longer be pointing to the north! I saw that not because of my terrible results but because I have a back up brunton compass which was pointing about 20 degrees off. I noticed that the wire ring under the moscow compass was bent so I straightened it up and now the moscow compass is only off by a couple of degrees but still, as you can imagine thats not good. Is there a way to replace that ring underneath the moscow or should I just toss the compass. Or is it the Brunton that's pointing the wrong way. I don't suppose there is a way to calibrate a compass, is there?
J.

That explains a lot!

Sure, you can calibrate it. Use Polaris, the north star and this magnetic declination calculator. Then go out at night with a flashlight (you may have to leave NYC to see Polaris, but its reasonably bright so give it a try). Then just look to see which of your two compasses points the correct number of degrees (west for NYC) from Polaris.

Polaris is less than a degree from the north celestial pole, so any time of night will do for this exercise. Max error will be +/- 0.7 deg. If you want to be more accurate, use this Local Sidereal Time clock. Be sure to set your location (Longitude is important here). When your LST matches the Right Ascension coordinate of Polaris (2 hrs 31 mins) or 12 hours later (14 hrs 31 mins), it is precisely aligned with geographic north.

You can use the big dipper to find Polaris (look at the chart on the wiki link above), or just use your compass to look approximately north. Polaris will be the same number of degrees above the horizon as your Latitude. A fist held at arm's length subtends about 10 degrees. For NYC, count up about 4 fists looking due north and the brighthest star (its not super bright) near that location is Polaris.

Wow, this is pretty interesting (from the Polaris wiki):

To the Bedouin people of the Negev and Sinai, Polaris is known as الجديّ al-jadiyy, "the billy goat".

That tells you, that when PG creates something one never knows how deep his thought process went.
On the topic of compass - I would like to know how much magetic north has shifted in 30 years for the Mt. Tom map?

It all stems from the G. It is the souce of all power in the universe. The One even derives his power from the G.

0.27 degress in 30 years for Mt. Tom, from 14 deg 6 mins in 1978 to 14 deg 22 mins today.

I had a related experience to Jeremy's. I keep a Silva Jet for periodic trips to the other hemisphere, and this last trip I thought it was more sluggish than it should be. Then at the start one day it told me to go back through the people who were waiting. After some perplexing minutes I found that treating south as north could at least let me find controls, though I had the suspicion that my bearings weren't too good. But it could have been me. It was still sluggish.

Anyway I had in my gear a really powerful magnet, its a "virtual thumb" for my MTB mapboard, but that's another story. I thought that if the compass had reversed polarity I might be able to persuade it back to reality by stroking the needle. What happened was that various bits inside the capsule came adrift from the pointer. And the compass was stuffed.

Now the possible connection with Jeremy is that hi-tech compasses get their speed by using tiny magnets located close to the pivot of the needle, to reduce inertia. The needle is just a bit of plastic that you can see easily, with the magnets stuck on the underside. Hence, they can become un-stuck, which I think is what happened to mine.

Moscow have high-stability compasses too, could it be that the magnets were coming unstuck? But I don't know them very well, or the significance of an external wire ring which can alter the reading.