Compasses

[Neo]

Bugger off DST.

The days are longer anyway! It's all about spending

[A Jay]

There is a method to use a watch face to determine north. Someone correct me if I'm wrong:

Point 12 at the sun, then north is between the hour and the minute hand [?]

Really? I'll have to test that out, that would be a very convenient trick.

I came across the method of brushing a sewing needle on silk so that it magnetizes, then hang it by some thread and the needle points to magnetic north. Or you could put it on a leaf and put the leaf in a puddle of water, and the magnetized needle will move the leaf and point magnetic north.

If your compass breaks down in the field, use the needle from the first aid or sewing kit to find magnetic north. I believe there's a way to magnetize the needle with battery too.

[Neo]

Requires confirmation.

I'd say my natural direction is within 15° anyway, but accuracy is important!

[Orion]

You can use a watch, although the instructions given above aren't correct. And you have to reverse the instructions depending on which hemisphere you're in. It's not going to be very accurate (probably about the same as my button compass). It becomes less accurate the closer you are to the equator. Cloudy days or dense tree cover make it more difficult and it doesn't work at night. With a digital readout watch you'd have to imagine a watch face and try to orient that way.

But better than nothing I suppose.

I thought the button compass was a good idea, at least in this instance.
My basic Silva baseplate compass weighs 25g. The button compass weighs 3.7g.

[Orion]

Someone did an analysis of the watch-as-compass technique.

He noted that how well it works depends on a number of factors, including latitude, time of day, time of year, and how close your watch's time is to the apparent solar time. For those living in counties with really large time zones (e.g. China) you'd really need to pay close attention to that last point.

He showed two graphs of the uncertainty, the first at about 49°N and the second at 25°N. The envelopes are the worst error for that time of the year; at a given time of day the error can be less (as is represented by all of the lines within each graph).


Error at 49°N


Error at 25°N

These assume that you have your watch perfectly calibrated and that you are able to align the sun with your watch with zero error -- that last one is going to remain a constant additional source of error.

You can see that it works better in non-summer seasons and the further you are from the equator. I was at 37°N and it was early September. So even if I had a watch adjusted for non-daylight savings time and I'd adjusted it further for the longitude (and I could align the sun with my watch perfectly) it appears it would have been no better, and probably worse, than my button compass. I had a lot of cloudy days and the times that I need the compass the most were when I was under tree cover. Plus my watch has a digital readout.

[ChrisJHC]

I have a small compass that fits onto my watch band. Also probably only accurate to +- 20 degrees but good enough for general direction. When I need more accuracy (rare) I pull out the Silva.


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[ChrisJHC]

Like this...

https://sep.yimg.com/ay/policestuff/tru ... ass-21.gif


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[A Jay]

Like this...

https://sep.yimg.com/ay/policestuff/tru ... ass-21.gif


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I was watching a tutorial on how to use a button compass by bushloreoz last night, and this looks like the same button compass he was using The square sides are good for orientating with a map:

https://www.youtube.com/watch?v=EjFf9I8UFlo

[Orion]

Suunto makes one like that. I saw it in a store and almost bought it as it so obviously worked better than my toy compass. But the store wanted $20 for it and at the time that seemed like too much.

Suunto claims an accuracy of ±5°. It even has a bezel which can be used to set the declination (to a resolution of about 7°). And they sell both northern and southern hemisphere models. Weight is 5g and that includes a clip to attach it to a watchband or whatever.

My toy compass responded slower and was less precise. If I had to do it again -- and I probably will take a button compass again on some trips -- I think it would be worth that $20 to me, or probably closer to $15 if I bought it online.

[GPSGuided]

On the watch method and a nice study. With errors reaching the +60 and -80 deg range, I say forget it. Mental assessment would probably be just as good or better.

[Son of a Beach]

There is a method to use a watch face to determine north. Someone correct me if I'm wrong:

Point 12 at the sun, then north is between the hour and the minute hand [?]

Not between the hour and the minute hand! North would go half way round every hour if you did that, and then suddenly jump back again, when the minute hand and hour hand were pointed in opposite directions.

Between the hour hand and the fixed 12 position.

NB: This method still works with a digital watch, smartphone or any other type of chronograph that doesn't include a round-faced watch with hands. You just have to know the time (from whatever source) and then be able to imagine where the round-faced watch hands and 12 position would be (or draw them in the dirt if your imagination is not that good).

The two problems with this method is that it's not much use if the sun isn't visible (ie, late night/early morning or bad weather) and it's not easy to get a very accurate bearing on North (if high accuracy is required).

[GPSGuided]

Ok, how about these other 2 ways on top the watch method? Just need relatively clear sky.

http://www.instructables.com/id/3-Ways- ... _page=true

[Neo]

Thanks for that all

[taipan821]

I must say, talking about compasses I've recently started using a lensatic compass. fantastic for precision navigation (I have to go on this bearing)
If you want a good quality sighting compass, K&R Meridian compasses are fantastic to use...just really, really, really expensive (sort of like the professional suunto compasses)

[Orion]

Is the lensatic compass more accurate than a mirror compass?

When I've needed to follow a bearing it was either in forest or in whiteout (several times I've found myself heading 180° from my intended direction). In either case there is nothing to sight.

A sighting compass would be preferable for triangulating ones position if clear landmarks are visible. Sometimes I wish I could do that more accurately than I am able to with my baseplate compass. Not that often though. Probably, for me at least, an ultralight GPS (or a phone app) would work better.

[A Jay]

I must say, talking about compasses I've recently started using a lensatic compass. fantastic for precision navigation (I have to go on this bearing)
If you want a good quality sighting compass, K&R Meridian compasses are fantastic to use...just really, really, really expensive (sort of like the professional suunto compasses)

Wow that K&R Meridan does look incredibly accurate! Although I read there is a big downside to mirror compasses, this article affirmed that they're unusable in the dark, or storm, or high winds, as you can't sight with the mirror in poor visibility conditions.

They said that for that reason, sighting compasses can't be relied upon on expedition like a baseplate compass can. Well this was a mountaineering group, they go with baseplate compasses for their reliability in all conditions.

[GPSGuided]

When I've needed to follow a bearing it was either in forest or in whiteout (several times I've found myself heading 180° from my intended direction). In either case there is nothing to sight.

A sighting compass would be preferable for triangulating ones position if clear landmarks are visible. Sometimes I wish I could do that more accurately than I am able to with my baseplate compass. Not that often though. Probably, for me at least, an ultralight GPS (or a phone app) would work better.

Fortunately or unfortunately these days, it's so much quicker to just jump on the GPS on the iPhone, feeling embarrassed and grossly under-utilising my Brunton and Suunto mirror sighting compasses in my collection.

[Orion]

...Although I read there is a big downside to mirror compasses, this article affirmed that they're unusable in the dark, or storm, or high winds, as you can't sight with the mirror in poor visibility conditions.

They said that for that reason, sighting compasses can't be relied upon on expedition like a baseplate compass can. Well this was a mountaineering group, they go with baseplate compasses for their reliability in all conditions.

When you can't sight a sighting compass is equivalent to a baseplate compass.

[A Jay]

...Although I read there is a big downside to mirror compasses, this article affirmed that they're unusable in the dark, or storm, or high winds, as you can't sight with the mirror in poor visibility conditions.

They said that for that reason, sighting compasses can't be relied upon on expedition like a baseplate compass can. Well this was a mountaineering group, they go with baseplate compasses for their reliability in all conditions.

When you can't sight a sighting compass is equivalent to a baseplate compass.

I had the same thought, that you could perhaps use a sighting compass like a baseplate compass minus the more accurate sighting feature. I don't know why the mountaineering club says they can't be relied upon. There's no baseplate with the direction of travel arrow, although I'm guessing the direction of travel arrow is more a convenience in that you can still tell which way is forward without it. Or perhaps I've misinterpreted their words.

Here is the the quote followed by the associated link to the article:


"Note: The heavy Silva Ranger compass, with bezel enclosed by a plastic cover and glass sighting mirror, is not the clear choice today. Backcountry users should not depend on a sighting compass, which is virtually unusable in the dark and in high winds, rain or driving snow. Learn to take accurate compass bearings from your waist. This enables you to look straight down on the needle to the "shed". This eliminates parallax"

"Note: The Silva Ranger compass adds only a heavy sighting mirror (which can not be used in dark and storm)"

http://www.traditionalmountaineering.or ... ompass.htm

[GPSGuided]

I had the same thought, that you could perhaps use a sighting compass like a baseplate compass minus the more accurate sighting feature. I don't know why the mountaineering club says they can't be relied upon. There's no baseplate with the direction of travel arrow, although I'm guessing the direction of travel arrow is more a convenience in that you can still tell which way is forward without it. Or perhaps I've misinterpreted their words.

Sounded like there's a bit of bias and subjectivity in those words. They all do the job with varying level of convenience, that's all.

[Mark F]

With a baseplate compass the most common way of using it for direction of travel is to align the travel direction (eg NE is 45 deg +- any adjustment for magnetic deviation) on the compass central capsule with the North South line that runs down the centre of the baseplate. Keep the compass needle aligned with the north arrow in the capsule and walk in the north direction pointed to on the baseplate - really couldn't be easier.

[GPSGuided]

Issue here is, most mirror sighting compasses these days have the same functionalities as a base compass. Sighting features are built on top.

[Orion]

Exactly. You don't have to use the mirror.

Note: The heavy Silva Ranger compass, with bezel enclosed by a plastic cover and glass sighting mirror, is not the clear choice today. Backcountry users should not depend on a sighting compass, which is virtually unusable in the dark and in high winds, rain or driving snow. Learn to take accurate compass bearings from your waist. This enables you to look straight down on the needle to the "shed". This eliminates parallax.

(http://www.traditionalmountaineering.or ... ompass.htm)

The potential for parallax error is an issue with many types of measurement -- including baseplate compasses.
What about the potential sighting error when taking a bearing from your waist?

The author says: "Learn to take accurate compass bearings from your waist".
That's like saying you shouldn't use a scope on a rifle but learn to shoot accurately from your hip instead.

You can also learn to minimize parallax error.

[slparker]

Why people are taking bearings from the waist is beyond me, as Orion states it is like shooting from your waist - both unnnecessary and inaccurate.

the only time you should need to follow a bearing from the compass without reference to the natural surroundings (dead reckoning) is in a whiteout or at night (or in close country I suppose) - in which case you will follow the bearing from reference to the compass at your waist, most likely. But the idea of shooting a bearing (i.e. taking a bearing to a distant object) from your waist makes no sense at all.

[GPSGuided]

With the neck cord on the compasses I have, none would allow me to work them at my waist level...

[taipan821]

Is the lensatic compass more accurate than a mirror compass?

I've never used a mirror compass so I wouldn't be able to say

[quote="A Jay", this article affirmed that they're unusable in the dark, or storm, or high winds, as you can't sight with the mirror in poor visibility conditions.

They said that for that reason, sighting compasses can't be relied upon on expedition like a baseplate compass can. .[/quote]

I've used my lensatic compass at night, I just open it up fully (which all lensatic compasses can do) and it functions like a normal baseplate compass, as for white outs....I don't get those in Nth Qld