Transit Compass

[Wayland]

I'd just like to say a big thank you to pteron and sargey for the Astro Navigation workshop they ran at the Moot, it was very useful.

One thing that came out of it for me was the use of certain compasses that could also be used to measure altitude.

One very nice tool for this we were shown was the Brunton pocket transit which is far beyond my budget unfortunately. A little poking around brought to light a new Composite version which is considerably cheaper (and lighter too) but alas, still a bit rich for my blood.

Anyway, I was looking for something completely unrelated on Dealextreme when up pops this wee beastie.



It appears to be a Chinese knock off of the Brunton with a price of around £26.... It's got to be worth a try at that price I reckon.

So my order is in and I'll let you know my impressions when it arrives.

 

[EdS]

would I be right in thinking when you say altitude you mean estiamting your height relative to a know feature? If so any compass with a clinometre can be used - to a great orr lesser accuracy, such as the Silva type 15
or Suunto MC2

This link has some good brieft descriptions:

http://www.zoom-one.com/distance.htm

 

[Gailainne]

You beauty, like you I've been looking around for a light weight or pocket version to play with, even the Davis Mk3 sextant, £50 tho . Looking forward to hearing how you get along with it. Interestingly it looks like it has bubble levels to help you with alignment. Reading the review it looks like it needs tweaked, and is easy to do.

 

[Wayland]

would I be right in thinking when you say altitude you mean estimating your height relative to a know feature?

As I understand it, altitude in astronomical terms is the angular height of an object over the horizon, azimuth would have been a better term.

If so any compass with a clinometer can be used - to a great orr lesser accuracy, such as the Silva type 15
or Suunto MC2

This link has some good brief descriptions:

http://www.zoom-one.com/distance.htm

That is indeed true, and we were also shown these. The Brunton type though really has this job nailed.

The other factor is that I have binned so many liquid filled compasses due to air bubbles that I really hate them now.

The Brunton is the best non liquid compass I've ever seen.

This is cheaper than the Silva 15 or Suunto MC2 and if it's even half as good as the Brunton I'll be very happy.

 

[Mastino]

That's a brilliant compass. It's the original version of the M2 Artillery compass http://www.olive-drab.com/od_soldiers_gear_compass_m2.php and very precise. I bought one back in the '80's and it was a extremely pricey.

 

[maddave]

Doesn't look bad for the money and the fix for needle weight and dampening etc written in the review seems straightforward.

 

[ged]

would I be right in thinking when you say altitude you mean estiamting your height relative to a know feature?

It's the angular altitude of something with reference to the position of the instrument. It's basically being used as a spirit level with a sight, and the angle between the very accurate spirit level and the sight is measured by a precision protractor.

 

[Wayland]

Doesn't look bad for the money and the fix for needle weight and dampening etc written in the review seems straightforward.

If anything, the fact that I can open the thing up and tinker with it makes it even more appealing for me.

I like things that I can fix or adjust myself without having to send half way across the world to get serviced.

It's the very thing that hacks me off about liquid filled compasses that gets a bubble just because I get it cold or climb a mountain, Gods forbid I ever fly with the damned things...

 

[EdS]

with you now. The compass might be worth a punt.

 

[pteron]

Let us know how you get on with it Wayland.

 

[Wayland]

Will do, I'm just wondering if it will get held up in customs.

I'm guessing there will be some duty to pay. (And probably an exorbitant handling charge from the post office.)

 

[ged]

... I've been looking around for a light weight or pocket version to play with, even the Davis Mk3 sextant, £50 tho

A bit of string and a plastic ruler can be a lot cheaper. There must be better writeups than this one but it gives you the idea:

http://en.wikipedia.org/wiki/Kamal_(navigation)

 

[pteron]

Ahh but what price fun?

(although that does remind me to make a Kamal and others for next year's workshop - ta)

 

[Wayland]

Looks like they make a damped version too.

 

[Laurentius]

On the subject of chinese knock offs, has any one bought one of those pound store Silva knock off's? I lost yet another compass yesterday (I'm not going to trust those nitize S biners any more for clipping anything to my belt loops) and I thought for a quid it either works or it doesn't. The immediate difference between it and the genuine article is that is is dry, not liquid filled, and not all that well put together, but it seems to point in the right direction so given my propensity for losing things, it's as well to have something in reserve. Whilst on the subject of poundland tat, some of it really is, I had one of those 9 LED torches, very bright and no mistake, but after leaving it in my car it fell apart when I took it out the other day.

 

[Spikey DaPikey]

If anything, the fact that I can open the thing up and tinker with it makes it even more appealing for me.

** Snip**

Gods forbid I ever fly with the damned things...

I think you need a plane to fly, not a compass

 

[Wayland]

 

[BOD]

On the subject of chinese knock offs, has any one bought one of those pound store Silva knock off's? I lost yet another compass yesterday (I'm not going to trust those nitize S biners any more for clipping anything to my belt loops) and I thought for a quid it either works or it doesn't. The immediate difference between it and the genuine article is that is is dry, not liquid filled, and not all that well put together, but it seems to point in the right direction so given my propensity for losing things, it's as well to have something in reserve. Whilst on the subject of poundland tat, some of it really is, I had one of those 9 LED torches, very bright and no mistake, but after leaving it in my car it fell apart when I took it out the other day.

Check every compas against a proven one preferably a good brand.

I have found knock-offs that were several degrees out and one that was 180 off. To with pasting the card I think

 

[Wayland]

It's just arrived so first impressions:

It's solidly made, all the joints are good with no sloppiness and in fact some are slightly stiff which means they should have some good wear time.

It's reassuringly heavy, it feels like it has a heft like the British army marching compass but I don't think it's quite that heavy.

As suggested on the site review, the Southern end of the needle was a little high but it was very easy to pop the o ring holding the glass and slide the copper balancing wire a smidge towards the point to level it out.

The needle does hunt a little but seem to be very sensitive, it's sitting on my desk by my keyboard at the moment and I can see very slight movements as I hit different keys. I don't think I've ever seen such sensitivity in a liquid filled unit. If anything it does remind you that to take an accurate readings you should move away from substantial metal objects, including you knife in some cases.

There is a slight rattle from the needle, not uncommon in dry compasses, but when closed the needle is lifted against the glass by a button and so is silent.

The button can also be depressed and released manually to help the needle to settle.

The long sight does not have a fixed vertical position when folded out from the body. I don't see any disadvantage to this arrangement. It's stiff enough to stay where you put it and if anything it gives you a wider angle of sighting positions.

One advantage that the Brunton has over this one is that the sighting line on the mirror also bisects the clear window, making alignment through the window slightly easier. Being used to peep sights I'm not sure that will bother me but it may be a consideration for some.

The bulls eye level seems accurate enough to level the compass and the long level on the clinometer is sensitive enough for degree measurements, possibly even half degree. I will test it's accuracy against a known level later.

The screwdriver that is supplied is slightly too thick for the declination screw so I'll talk about that a bit later too.

 

[Wayland]

Just been out in the workshop fixing the screwdriver, and a useful little detail came literally to light. there are luminous spots on the North side of the needle, the quadrants of the scale and the declination adjustment point.

With the screwdriver fixed, the declination screw moves the entire scale east or west. I only need 2° 02' W adjustment where I am (See correction below.) but the scale is marked for 30° either way. Incidentally, the small screwdriver head on the can opener of my SAK is thin enough to adjust this screw if needed.

On the Astro Nav talk, pteron mentioned the main problem with using these for star sights was not being able to see the level in the dark. I had a hunch about that which does look like it will work.

The levels are filled with a flourescent liquid as is common practice. So a small UV emitting mini led torch, pointed into the compass makes the level very clear in the dark while not disrupting night vision too much.

Although holding it is a little awkward it does seem to address this problem quite well.

( Checking the NOAA declination calculator site instead of the calculation based on the OS map gave a declination of 2° 40' W. see post below for details.)