Put your compass in hot (not boiling) water will reduce or even remove air bubbles. Thats what I do occasionally.

Only temporarily. Expose the compass to low temperature and/or low air pressure (at high altitudes) again and the bubble will grow back IME.

Nevertheless, it is a quick fix for a little while at least. Also, that's why it's a good idea to carry a compass close to your body on winter treks and in the mountains - keep your compass warm and there's less chance of a bubble forming inside the capsule.

Checked out my compass this weekend, and my worst fears were realized. Apparently I either need a safer carry mode for my compass when not in use or a way to protect it in the pouch. When I checked it, at first I thought it was A-ok, no bubbles, then I noticed the needle was a bit wonky. Closer inspection revealed a cracked plastic casing that had allowed all the fluid to escape. Sad part is, I'm not sure how long it's been that way. I've recently picked up a new day pack that will hopefully give me the option to tuck a future compass safely inside the pack when it's not being used. I may also put it in some kind of hard plastic case or maybe an altoids tin for additional protection.

Its not really how old the Topo Map is, it how accurate it was when it was made and how much has changed in the area since. Accurate Map with very few changed = Good Useful Topo. Still given a choice I would take a Topo updated last year in comparison to one made 30 years ago.

Only 30 years? Working at Channel Islands National Park, I used topo maps that were produced in 1943. .The basic topography from that era is still in use today, more than 70 years later. Using them routinely from 1982, I found that the topography was usually spot on. Not so with cultural features, but that is why you carry a pen and pencil.

Interestingly, although the islands held still for their photos in 1943,the maps show nothing of the military camps and fortifications that existed at that time.

This situation is true for a lot of wild spots, at least in the western US.

The very best thing to have is good, sharp copies of aerial photographs. They typically are date stamped, and even for out of the way places like the Channel islands (US)there is now a plentiful selection.

The best map of the Channel Islands NP is National Gepgraphic's Trails Illustrated #252 - Channel Islands National Park. It is current on both topography and culture, but is still essentially the 1943 aerial photography. This is probably the case for many areas in this series.

You can never have too many maps/photos....

A bubble has almost no effect on the dampening quality of the rest of the liquid, nor on the compass' precision. In fact, it gives you an advantage at holding the compass naturally horizontally (working like a bubble level).

Also, I doubt that a hiking compass must be of a top quality overall as soon as it offers good enough rigidity of the casing and the needle axis is concentric with the dial. The rest is just your skills.

By the way, if the bubble is interfering with your aesthetics sense - use a round sticker in the middle of the top glass. If you don't see the bubble you are staying calm and your compass is leveled - exactly what you need to read the compass reliably.

I've got this http://www.ebay.com/itm/New-Professional...g-/281643293201 cheap model not so long ago and love it for map working, as it is much more precise and convenient to use than, lets say, a mirrored Brunton for $50. With that construction you are looking at the dial from the side through the integrated regulated dioptric loupe, not over a confusing and too close mirror, so you see the target, the readings, and the levelness quality simultaneously in focus. No more frustration trying to see something through the narrow slit in the mirror, the lid's window of this one is fully transparent. Also it has a photo tripod mount hole in the bottom, I'm sometimes using it on my hiking stick (which has a hidden photo head), when I want to make an exceptional azimuth fix. All metal casing, even though a bit clumsy finished.

Yes, I have used some very old ones as well. As long as you know the current declination for converting you magnetic azimuth to grid, and visa versa, then you are good to go. It gets really interesting when you are using some ancient mining maps produced in another language in a country where quality control does not exist. Makes for some interesting walks.

Sorry to burst anyone's bubble, but I have to disagree on pretty much all counts.

A large bubble can and will destroy the accuracy of a liquid-filled compass. The accuracy of a compass depends on the ability of a small magnetized needle to swing freely and point to magnetic north. The magnetic force that orients the compass needle is tiny, so it is important to ensure that the compass needle can turn without the slightest hindrance. That's why any decent compass will have a small jewel (usually sapphire) bearing to ensure a smooth needle movement.

A bubble inside a liquid-filled capsule essentially acts as an air pocket trapped against the housing. If large enough, it will block the movement of the compass needle and push it around forcibly as you move the compass and the bubble begins to shift back and forth. Once that happens the needle will no longer point north consistently. Instead, you will be getting totally random bearings with no way of knowing if any of them is actually right.

I don't speak about this from theory. I have seen it happen in real life and have done a fair bit of land navigation in my time, sometimes under pretty demanding conditions. YMMV but in my experience it is a scary proposition to be caught out in the wilderness with a compass you can't trust and no other effective navigation aid when you really need it.

There is absolutely no advantage to having a bubble in your compass. Other than highly specialized surveying compasses (usually prismatic type) that make use of a spirit bubble (attached separately to the compass housing) there is absolutely no point in adding that feature to a general purpose compass. Same for a photo tripod mount - what the heck is that all about? I see these features becoming more and more common on the cheap Chinese compasses sold lately. In reality, it's nothing more than a pathetic attempt to attract uninformed customers who'd be much better off getting a quality compass from a reputable manufacturer.

Actually, the eBay special on your link is a pretty obvious example of a low quality Chinese knockoff. As a matter of fact, I know that particular model well, it seems to be very common these days. I would not rely on that compass under any circumstances. The build quality is very low and the "advanced" features are a joke. I've had an opportunity to test three identical examples a couple of years ago. None of them would point north accurately, each was off by up to 10 degrees IIRC. Then again, not sure what more one could expect from a "New Professional Pocket Military Army Geology Compass for Outdoor Hiking Camping"?? Honestly, you would be much better off with any inexpensive baseplate compass made by a decent brand if money is a concern.

This probably is asking for something nonexistent, but are there any controlled studies demonstrating the accuracy/inaccuracy of bubbles in a compass? What would be critical would be the magnitude of introduced inaccuracy. For many purposes, a surprisingly amount of inaccuracy is quite tolerable.....

That's my point exactly. In fact, you can't expect a precision better than 10 degrees. Because anything you can get from a typical baseplate compass will have a comparable error introduced by its very design, dictating a certain overly inaccurate measurement technique. The cheap compass, I showed above, is having many of the issues of a typical ancient design resolved quite well. Yes, the parts are cheaply made, but they are doing what they supposed to do at improving the accuracy compared to any fancy plastic baseplate type. But I can easily agree that the 0 mark of its azimuth dial may be off by a bit. Though, I have checked mine for concentricity (mount it on a tripod in the open field, take a fix to one object, go around the compass and see what's exactly in the opposite direction (it has symmetrical sights), now rotate the compass on the tripod to point to that second object, and compare the new fix with the first one, must be 180 deg difference), it's ideal. And that's all what truly matters for a good compass mechanics. I don't mind correcting for the magnetic declination, so if I'll find that my dial is off for some degree, I will just use that delta along with the declination correction. Know your gear before you go anywhere.

Regarding the bubble, sure thing, if it's touching the sides already - the compass is defective and not usable, as the needle ends will be floating. I'm talking about rather small bubble, which is significantly smaller than the needle's length.

For the leveling - have you ever hiked in the steep hills with a compass? Especially liquid filled compasses may have problems there, as you have no natural sense of leveling it standing on a slope, and any equilibrium movements of the needle itself are effectively dampened. Leveling of any compass is very important if you are taking bearings to align with the map or directions list. A dedicated bubble level is nothing special and easiest to use leveling aid on the go.

Tripod mount for the compass is a godsend for triangulation, when you need to measure a distance, locate yourself precisely on the topo map between the benchmarks, or need to create such a map from scratch. Sure thing, for going out of the bush to a road a button compass on your watch band will do just fine.