Product description - general

This is a small oil-filled compass with a rotating capsule, set in a small rectangular plastic base. The base includes a low-power 22 mm (~5/8") plano-convex magnifying lens and engraved scales on the underneath along the two sides - one metric, one imperial. (The current model shown on the web site has a third scale across the front edge, and they may be slightly different scales.) There are holes in the two rear corners for a loop of string, and those corners are rounded and curved up slightly to minimise any tendency to dig into your body when the compass is hung around your neck. The DO 110 unit is identical except it does not have the moulded-in lens.

The outer ring of the capsule is black with white graduations in one degree increments. It rotates in the base and the base has a North mark, so the capsule may be set to compensate for the local magnetic declination. (The North mark is invisible in the image here having lost its pigment years ago.) There is a form of coarse knurling around the capsule which allows a good grip for ease of rotation. The base of the capsule is transparent with parallel red lines aligned N-S relative to the outer scale. There are two red bands on the lines closest to the pivot, one on each side, which allow me to align the compass needle parallel to the lines with about one degree accuracy.

The needle is marked red at the N end and white at the S end. The pivot appears to consist of a hardened steel pin set in the base and a jewel (sapphire) watch bearing set in the needle. (The Swiss have a lot of experience with such watch bearings.) There is a slight recess in the plastic lid which forms the top of the capsule, and this matches the top of the pivot boss on the needle. It serves to limit the movement of the needle off the pin when tilted, and is shown in the diagram below. There is no fluorescent paint on the needle.

 

Product description - technical

The needle is about 29 mm (1.1") in length, 2 mm (0.7") wide and about 0.5 mm (0.025") thick. The length appears to be quite sufficient to give it adequate magnetic torque to overcome any friction at the pivot. The low thickness lets the needle rotate fairly quickly through the oil, but there is enough drag that the needle is only slightly under-damped at typical room temperatures. The oscillation dies in about two full cycles. Under very cold conditions the oil becomes a little more viscous and the damping increases slightly, but since I normally hang my compass around my neck inside my clothing it doesn't normally get that cold.

The pivot boss is of medium size, about 4 mm (0.15") in diameter. It is hard to measure the height of the pivot point above the plane of the needle: I estimate it to be about 2 mm (0.07"). There is a solid ring of metal below the needle around the pivot, shown in the diagram as the 'Lower weight'. This is quite important for the usability of the compass in different countries around the world.

The capsule is retained in the base by a small wire spring right around it. This spring can be removed (with care and some difficulty) to separate the capsule from the base. This allows the rotating bearing to be cleaned out. Doing this prevents wear in the plastic bearing and maintains the right level of bearing friction, which in turn helps maintains the preset declination.

 

Field information

Most of our walking is done off-track in rather complex country, and continuous and accurate navigation is usually essential to avoid 'geographical embarrassment'. The compass fits quite well in my hand for those times when I need to follow a precise bearing. The damping is sufficient that this is easy to do. While some people like a heavy compass for this sort of work to help stabilise the unit in one's hand, I have not found the light weight to present any problem - and it is easier to carry for long periods than a heavy brass military prismatic unit!

The flat base lets it rest on a map easily. I normally align the side of the compass with the grid on the map and then rotate the assembly until the needle is aligned with the red lines in the base. As mentioned above, I can align the compass and the map to about one degree in the field this way. I have yet to experience a practical navigation problem which required anywhere near that accuracy, even in the most difficult country. It is always sufficient to allow me to locate nearby ridges and valleys by extrapolation from the map and to determine our course. While there are many larger and more complex compasses (and more expensive!) on the market, I do not believe any of them would be of any greater utility to me.

On the other hand, I do have smaller compasses, but I have found they are much more difficult to use in practice. Much care is needed with the middle one to be sure of the bearing: it has to be 'very' horizontal to avoid drag on the needle. The smallest one is not really reliable: there is so little torque on the very short needle that it jams far too easily. My conclusion is that the size of the DO 150 is about optimal for serious off-track navigation in our country.

Some more expensive compasses include a means for 'sighting' on a distant point while reading the bearing. Taking several such readings allows you to triangulate your position on a map (or to establish where the enemy is so you can fire a cannon at them). However, for several reasons we very seldom use triangulation. Australia is an old country and the 'mountains' are usually eroded down to round lumps, so there are few good points to take bearings off. The scrub is frequently sufficiently thick that it blocks long distance views all around. The terrain where we do a lot of walking tends to be more of a dissected plateau, with no obvious peaks to mention, and often we are in a narrow valley following a river rather than up on a ridge. Anyhow, around here travelling for so long without careful navigation that one needs to establish one's position by triangulation is usually a recipe for disaster. Other users in other sorts of country may find triangulation more useful.

The two holes and rounded corners work well. I hang the compass around my neck on a loop of cord, and the fact that there are two holes at the corners rather than one in the centre means the compass always hangs flat against my chest, with the larger flat side against my chest. I have never been conscious of the corners, so the rounding might be of some use.

The capsule appears to be well sealed and I have not seen any air bubbles appear inside it. While such air bubbles do not affect the accuracy of a compass, they don't look so good. Recta makes a model which actually 'features' a bubble: it can be used as a spirit level as well. However, sighting along the edge of the compass while looking down at the bubble presents some anatomical difficulties.

The magnifying lens is of low power and I rarely use it. I never use the scales along the sides, which is just as well since these lost the pigment marking out of the engraved (or embossed) lines years ago. I suspect that the pigment has been rubbed off by my skin and sweat since the underside of the compass normally rests against my chest. The N line for the rotating ring has also lost its pigment, which makes setting the declination just a little more difficult. However, the embossed line is still visible in transmission and the capsule rotation is reasonable tight, so that I do not need to adjust the declination setting more than about once every six months.

The absence of any fluorescent paint markings does not worry me at all. For a start, experience shows the paint does not last more than a few years. More importantly, I try very hard to be in my sleeping bag before it gets that dark. On the rare occasions when I have had to travel at night I have used the stars. (Here in Australia we have a very convenient arrangement of stars called the Southern Cross and Pointers which accurately point to the South Celestial Pole.)

 

International use

A common question is whether a compass bought south of the equator can be used north of it, or vice versa. The reason for the question is the tilt in the Earth's magnetic field. In Australia the field points up at a significant angle, while in North America and Europe it points down. I have often seen comments that the needle has to be weighted at one end or on one side to overcome a tendency to align with the tilt of the field, so that one needs a Northern hemisphere compass and a Southern hemisphere compass. There are even some comments like this on the Recta web site - in the section where they are promoting a far more expensive 'global' version.

To put it politely, these comments are wrong. I bought this compass in Australia, and I have have used it in Nepal, the UK and France with complete success. I have also bought similar compasses in the UK and France, and used them in Australia. So have many other people. Theory gives way to experiment.

The reason for this lack of sensitivity to the tilt in the magnetic field lies in the design of the pivot, as shown in the above drawing. The centre of support is about 2 mm (0.07") above the plane of the needle, at the tip of the pin, while the Centre of Gravity (CoG) of the needle lies well below the plane of the needle. In effect, the needle hangs 'down'. That is a major reason for the heavy metal ring I mentioned before: it lowers the CoG. (Another reason for the presence of the ring is to stop the needle tilting very far when hanging around your neck, but that could be done with a far lighter ring.) The torque due to the tilted magnetic field is actually very small - and so of course is the torque aligning the needle in the N-S direction. In practice the needle tilts maybe a degree or two before the effect of gravity balances things out. (Yes, I have measured this.) Given the normal use in the field, I doubt anyone would ever be conscious of this.

Servicing

I have been using this compass intensively for many years. In that time I have once separated the capsule from the base and cleaned the capsule bearing. Otherwise I have done nothing to it. And it does not need batteries.

Negative aspects

The loss of the pigment over time is the only negative aspect. I have done nothing about it as it does not affect my use of it.

Summary

Would we buy another?
Certainly I would buy another compass of this size. I would not waste money on a more complex unit, but I would also hesitate to go much smaller. As many other companies sell compasses very similar to this model, I see no reason to be especially loyal to this brand. But then, it has worked well.

Addendum 2004

My wife and I took this compass to Europe in 2004 on an eight-week walk along the Pyrenees. We went along the GR11 in Spain from the Atlantic to the Mediterranean and then back along the GR10 in France from the Mediterranean to Merens on the Ariege river. As outlined above, once again it worked perfectly well North of the Equator, just as it had in Australia.

 

Biographical information

Name:	Roger Caffin
Age:	57
Gender:	M
Height:	1.66 m (5' 5")
Weight:	63 kg (138 lb)
Email:	r dot caffin at acm dot org
Location:	Sydney, NSW, Australia

Backpacking Background:

I started bushwalking (the Australian term) when I was about 14 yrs old, took up rock climbing and remote exploration walking at University, later on took up ski touring and canyoning. These days I do all my trips with just my wife. Our preferred walking trips in Australia are long ones: about a week in the general Blue Mts (east coast of Australia) and Snowy Mts (alpine) regions, and up to two months long in Europe and the UK. We favour fairly hard technical trips in remote country and prefer to travel fast and light. Our ski touring trips are usually 5-7 days long as well, with full packs and tents. In between we still do fairly long day trips: it's a form of relaxation. Having discovered that 20 kg (44 lb) packs are no longer fun, we have become believers in ultra-lightweight walking. Typically we carry an ultra-lightweight tent (we need full insect proofing here), Therm-a-rest mattresses, lightweight sleeping bags, lightweight packs, a lightweight butane/propane stove, light climbing rope (frequently used) and very light parkas. I would carry about 12-14 kg (26-31 lb) total for a week, my wife would carry a bit less (more when skiing of course).

I am also the maintainer of the Australian aus.bushwalking FAQ web site www.bushwalking.org.au/FAQ/.