All about compasses: buy Magnetic South, set the declination, find your way.

A compass is a magnetised needle on a pivot, and two things about it catch people out in Australia. The first is that the needle has to be balanced for the Southern Hemisphere. Silva marks those compasses MS, for Magnetic South, and Suunto marks them SH. It sounds like a joke, in the same family as the left-handed screwdriver, and it is real: a northern compass tilts and drags here. The second is that the needle doesn’t point where your map does. From Brisbane to Melbourne it sits 11 to 13 degrees east of true north, and walking a map bearing without allowing for a 12-degree gap puts you about 200 metres off course for every kilometre. This guide explains both, says what to check before you buy, and finishes with four techniques that stop a small error becoming a lost afternoon.

How a compass works

The Earth has a magnetic field, and a compass needle is a small magnet balanced on a pivot so that it can turn freely. Left alone, it swings round until it lies along the field. The capsule around it is filled with liquid, which slows the needle so that it settles in a second or two and doesn’t keep swinging.

One correction to the usual story: the needle does not point at the magnetic pole. The US government’s geomagnetism service puts it precisely: a compass lines up with the horizontal part of the magnetic field at the place where the compass is, and not to any single point. Most of the time the difference is academic. It matters for the two things this page keeps coming back to. The field is not horizontal, which is why needles are balanced by hemisphere. And it does not run exactly north–south, which is declination.

One thing does not change: the red end of the needle points to magnetic north everywhere, Australia included. A Southern Hemisphere compass is not a compass that points south.

The parts of a baseplate compass

The baseplate compass is the kind you use with a map, and Silva calls it the most common type. Everything else on this page assumes you know its parts.

• Baseplate. Clear plastic with straight edges, a ruler and map scales. The long edge is what you lay along your route on the map.
• Direction-of-travel arrow. It points away from you, along the line you are going to walk.
• Rotating dial (also called the housing or bezel). It is marked in degrees, 0 to 360, clockwise from north. You read the bearing at the index, where the dial meets the direction-of-travel arrow.
• Orienting arrow and orienting lines. These are printed on the floor of the capsule and turn with the dial. On the map, you line them up with the grid lines.
• Needle. The red end points to magnetic north.

The orienting arrow has a nickname, the shed, because of the one instruction everybody remembers: put red in the shed. Turn your whole body until the red end of the needle sits inside the orienting arrow. Once it does, the direction-of-travel arrow points along whatever bearing is set on the dial.

Other shapes do parts of the same job. A mirror compass (or sighting compass) adds a hinged lid with a mirror, so you can see the dial and a distant landmark at the same moment. A thumb compass straps to the thumb and is held against the map; Orienteering Ireland describes it as the choice of orienteers who work from a mixture of map and compass, with the baseplate preferred by those who take accurate bearings. Clip-on and pocket compasses show direction only and are backups.

Why Australia needs a Magnetic South compass

The Earth’s magnetic field lines are not parallel to the ground. They tilt into the ground more and more steeply as you approach a magnetic pole, and at the poles they are vertical. A needle that was free to follow the field completely would follow that tilt, with one end pointing at the dirt. North of the magnetic equator it is the north end of the needle that dips. South of the magnetic equator it is the south end.

A compass is only useful if the needle floats level, so the makers counterweight it. In the Northern Hemisphere the weight goes on the south end of the needle. In the Southern Hemisphere it needs to be on the north end. Bring a northern compass to Australia and the weight is on the wrong end, adding to the tilt it was meant to cancel.

Silva’s own description of the result is restrained: in the wrong zone the needle may tilt and give a less accurate reading. A tilted needle can also rub on the capsule, which makes it slow to settle and inclined to stick, and a compass that sticks will show you a confident wrong answer.

What the letters mean

Silva balances its compasses for one of three zones: MN, ME or MS. Suunto uses two zones, northern and southern, which overlap by several degrees, and notes that four or five zones used to be needed. Both also make global needles for travellers. In Suunto’s design the magnet tilts independently of the needle, so the needle stays level anywhere, and the compass still works when held up to about 20 degrees off level.

Where the trap is

The same model is sold in more than one balance under almost the same name. Silva’s international website says plainly that it mainly sells compasses for the northern zone, and its product pages for all three Silva compasses on this page list “Magnetic north (MN)”. An overseas seller, or a marketplace listing that doesn’t mention a zone, will most likely send you a northern compass.

So look for the letters. MS should be in the product name, as in “Silva Expedition MS”. For Suunto, look for SH, as in “Clipper L/B SH”. If you cannot find either, ask the seller before you pay. When the compass arrives, hold it level and turn slowly on the spot: the needle should swing freely, stay level and settle quickly.

Three norths, and the angles between them

Once the needle is level, the next surprise is where it points. A walker with a map has three different norths to deal with.

• True north is the direction to the geographic North Pole, the top of the axis the Earth spins on.
• Grid north is the direction of the vertical grid lines printed on the map. Flattening a curved Earth onto a flat sheet means the grid can only line up with true north along the middle of each mapping zone. Away from the middle the two drift apart slightly, by an angle called the grid convergence. The Melbourne Bushwalkers’ navigation notes give almost nothing in the Victorian Alps, 0.8° at Marysville and 1.7° in the Brisbane Ranges.
• Magnetic north is where the needle points.

Two angles matter. Magnetic declination is the angle between true north and magnetic north, counted as east when magnetic north lies east of true north. You will also see it called magnetic variation. The grid-magnetic angle is the angle between grid north and magnetic north, and it is the one bushwalkers use, because bearings are measured off the map from its grid lines.

You don’t have to work either out. They are printed in the margin of a topographic map, usually as a small diagram of the three norths. Victoria’s official maps, for example, are aligned to grid north and show the grid convergence and magnetic declination calculated for the centre of each sheet.

Declination around Australia

These figures come from the magnetic field calculator run by the US National Oceanic and Atmospheric Administration, using the World Magnetic Model (WMM-2025), for 2 October 2026. The model gives its own uncertainty as about a third of a degree.

Two cautions. First, this table is measured from true north. The grid-magnetic angle on your map will differ from it by the grid convergence, so take your working figure from the map margin. Second, the field is slowly changing. In Australia the change is gentle at present: the same model has every place in the table moving by 0.06° a year or less, so even the fastest of them, Hobart, takes more than fifteen years to shift one degree. A recent map is fine. For an old one, check the date in the margin and look the figure up afresh.

Grandma’s Socks and My Green Apple

A bearing measured on the map is a grid bearing. A bearing the compass can follow is a magnetic bearing. Across most of Australia magnetic north lies east of grid north, and in that case two rules convert one into the other:

• Grandma’s Socks (GMS): Grid to Magnetic, Subtract. Going from the map to the compass, take the grid-magnetic angle off.
• My Green Apple (MGA): Magnetic to Grid, Add. Going from the compass to the map, add it on.

Australian navigation guides set out the GMS and MGA rules in exactly these terms, and the Melbourne Bushwalkers’ notes record “GrandMa’s Socks” in so many words. The words hung on the letters vary from club to club (“My Great Aunt” is another MGA, and some versions don’t bear printing). Use whichever you will remember at four in the afternoon in the rain.

Map to ground. Your map gives a grid-magnetic angle of 12° east. You measure the bearing to the hut on the map and get 070°. Grandma’s Socks: 070 − 12 = 058°. Set 058 on the dial and walk.

Ground to map. You sight a peak with the compass and read 100°. My Green Apple: 100 + 12 = 112°. Draw a line on the map at 112 through the peak, and you are somewhere on it.

If you forget which is which, do what the Melbourne Bushwalkers’ author does and picture the little diagram: grid north straight up, magnetic north leaning to the right of it. Any direction is a smaller turn from the right-hand arrow than from the upright one, so the magnetic bearing is the smaller number.

The Western Australian exception

The two rules assume magnetic north is east of grid north. That holds for the eastern states, South Australia, the Northern Territory and most of Western Australia. Along the west and south-west coast it flips: magnetic north sits slightly west, about 1.5° at Perth and 1.6° at Albany. There the angle is negative, and as one Australian guide puts it, subtracting a negative angle increases the bearing. Where the angle is that small, the grid convergence can be as large as the declination, so the only safe source is the diagram on the map in your hand.

For the same reason, be wary of rules of thumb from overseas books and videos. They are written for places where magnetic north may lie on the other side, and they can be exactly backwards here.

How much does it matter?

One degree of error moves you about 17 metres sideways for every kilometre you walk. Skip a 12° correction and you are about 200 metres off after one kilometre, and 400 after two. In open country you might still see your target. In thick bush you will walk straight past it.

Adjustable declination: let the compass do the sums

On a compass with adjustable declination, the orienting arrow is not fixed to the dial. A small screw turns the arrow a few degrees east or west of the dial’s north mark. Suunto describes it as set once, by turning the north arrow in the bottom of the capsule to your local angle, with a small screwdriver supplied for the job. Silva calls the same thing a built-in permanent adjuster.

Set it to the grid-magnetic angle printed on your map, and the shed now sits that many degrees to the side of north on the dial. When you put red in the shed, the needle is on magnetic north and the dial is on grid north. The compass has done Grandma’s Socks for you.

From then on a bearing taken off the map is walked as it is, and a bearing sighted in the field is drawn on the map as it is. Three cautions:

• Don’t correct twice. Once the compass is set, leave the socks and the apple at home. Doing the arithmetic as well puts the whole error straight back in, the other way round.
• Reset it when you travel. Sydney is 12.8° east, Adelaide 8.1° east and Perth 1.5° west. As Suunto says, the setting holds until you move to a place with a different declination.
• Check it before each trip. It takes five seconds to see that the shed still sits on the right number.

Cheaper compasses often carry a fixed declination scale instead: a second set of degree marks inside the capsule. Nothing moves. You take the bearing as usual, then turn until the needle points at your local angle on that scale, where you would otherwise have put it in the shed. It works, but you have to remember to do it every time.

Taking a bearing from the map: one, two, three

Silva teaches this as its 1-2-3 system, and it is the same three moves on any baseplate compass.

1. Place. Lay the long edge of the baseplate on the map so that it joins where you are to where you want to go, with the direction-of-travel arrow pointing towards the destination.
2. Turn. Hold the baseplate still and turn the dial until the orienting lines are parallel to the map’s north–south grid lines, with the orienting arrow pointing to the top of the map. Ignore the needle for this step. The number at the index is your grid bearing.
3. Follow. Lift the compass off the map and hold it flat in front of you with the direction-of-travel arrow pointing straight ahead. Turn your whole body until red is in the shed. The arrow now points at your destination.

If your compass has no declination adjustment, there is one extra move between steps 2 and 3: apply Grandma’s Socks, and turn the dial to the smaller number.

Don’t walk staring at the needle. Look along the arrow, pick something on the line (a tree, a boulder, a notch in the skyline), walk to it, and repeat. To go the other way, from the ground to the map, point the arrow at a landmark, turn the dial until red is in the shed, read the bearing, apply My Green Apple if you need to, and lay it on the map.

For everyday walking you will take fewer bearings than you expect. Turning the map until it lines up with the country around you, and keeping it that way, does most of the work. Geoscience Australia’s free Map Reading Guide covers the three norths and using a compass with a topographic map, and is worth downloading.

Buying guide: five checks, four compasses

Five checks before you pay

1. MS, SH or global. This comes first because nothing else matters if the needle drags. The letters should be in the product name. No letters, no sale, until the seller confirms.
2. A rotating dial marked in degrees, on a baseplate with a straight edge. Without both you cannot take a bearing from a map. Clip-on and pocket compasses show you which way is north, and that is all.
3. Adjustable declination. Between Brisbane and Melbourne you are correcting for 11 to 13 degrees on every bearing. Having the compass do it removes the most common mistake in map and compass work.
4. Scales that match your maps. The scales on the baseplate turn a distance on the map straight into metres. Australian bushwalking maps are mostly 1:25,000 or 1:50,000 (Victoria’s official series, for one, is published at 1:25,000, 1:30,000, 1:50,000 and 1:100,000), so look for those two.
5. Mirror or no mirror. A mirror lets you sight a distant feature more precisely, and Silva suggests sighting compasses for open terrain where precision over longer distances matters. It also makes the compass thicker. In forest, where you rarely see far, a plain baseplate does everything you need.

One thing not to buy: cheap button compasses

The cheap button compasses, the tiny ones sold loose or by the dozen for a few dollars, will drive you crazy. Don’t buy them. They are not worth your sanity.

Some people do buy a dozen, test each one against a compass they know works, and throw out the duds. That is a strategy. We would rather spend a bit more and get one of good quality, because when you need a compass, you really need it to point the right way.

Small is not the problem. The two backups below are both small. Cheap is the problem.

A bubble can turn up, whatever you pay

Spending more does not buy you out of everything. Any of them can develop a bubble in the capsule over time, even the expensive ones. A bubble is not a sign that you bought the wrong compass.

Trail Hiking Australia’s guide to compass bubbles gives the causes. The liquid shrinks in the cold, so a compass filled in the warm can show a bubble on a frosty morning. Thin air at altitude makes any trapped gas expand. And over the years seals wear and plastic turns brittle, faster if the compass lives in the sun or in a hot car. The same guide’s test for a harmless bubble is a good one: it is small, it does not touch the needle, and the needle behaves exactly as it did before. If the bubble keeps growing, or the needle starts to stick or drift, replace the compass.

Four compasses

Two are small backups and two are full navigation compasses. The Silva Expedition and Expedition S are the two we own and use.

Clip-on backup

Suunto Clipper L/B SH

What it is for: a glance at which way you are heading without taking anything out of your pack. It clips to a watch strap, a sleeve, a pack strap or the edge of the map.

Balance

SH version (an NH version is also sold)

Size

30 × 24 × 11 mm

Weight

5 g

Dial

Rotating bezel, 10° steps

Card

Liquid filled, luminous cardinal points

Declination adjustment

None

Made in

Finland

Know before you buy: it comes in NH and SH versions with almost identical names, so make sure the one in your basket says SH. With a bezel marked every 10 degrees it will tell you that you are still heading roughly north-east. It will not walk you to a boulder on a bearing. When we checked on 2 October 2026, the Clipper listing on Amazon Australia did not say which hemisphere it was balanced for, so we have linked to Suunto’s own Australian store, where the SH version is a named option.

See the SH version at Suunto

Pocket backup

Silva Pocket (MS)

What it is for: a spare in the pocket or clipped to a zip, for the day your main compass is at the bottom of the pack or at the bottom of a creek.

Balance

MS version sold in Australia

Size

57 × 47 × 9 mm

Dial

Cardinal directions

Extras

Thermometer (°C and °F), carabiner hook

Declination adjustment

None

Silva rates it

Basic

Know before you buy: it is a direction finder, not a tool for taking bearings from a map. Silva’s own product page lists the MN version, and the Amazon Australia listing we checked on 2 October 2026 did not name a zone at all. The link below goes to an Australian map shop whose listing states Magnetic South.

See the MS version at Mapworld

Baseplate compass · one of the two we use

Silva Expedition MS

What it is for: map and compass navigation. You take bearings off a 1:25,000 or 1:50,000 map with it, walk them, and set the declination once.

Balance

MS

Type

Baseplate

Declination adjustment

Yes, built-in permanent adjuster

Map scales

1:25,000, 1:40,000, 1:50,000, mm and inch

Clinometer

Yes, for slope angle

Extras

Magnifier, luminous markings, scale lanyard, slope card

Size

12.7 × 6 × 1.3 cm

Know before you buy: Silva’s own page for this model lists the MN version, so the letters MS in the product name are what you are looking for. Silva pitches the Expedition range at experienced users, and its Field and Ranger ranges sit below it; those are sold in MS versions too, and the five checks above apply to them just the same.

See it on Amazon AU (paid link)

Mirror sighting compass · the other one we use

Silva Expedition S MS

What it is for: everything the Expedition does, plus precise bearings on distant features. You open the lid to about 45 degrees and see the landmark through the sight and the dial in the mirror at the same time.

Balance

MS

Type

Mirror sighting, with sighting hole

Declination adjustment

Yes, built-in permanent adjuster

Map scales

1:25,000, 1:50,000, mm and inch

Clinometer

Yes, for slope angle

Extras

Magnifier, luminous markings, scale lanyard, slope card

Size

10.8 × 6.4 × 2 cm

Know before you buy: the S is shorter and thicker than the plain Expedition, and you open the lid right out for map work. As with its sibling, Silva’s own page lists the MN version. A mirror also gives you a way to signal with reflected sunlight.

See it on Amazon AU (paid link)

Side by side

If you are buying one compass to learn on and keep, buy a baseplate compass with adjustable declination, in MS. Add a clip-on or pocket compass later as a spare. A second compass is also how you find out that the first one has been damaged, which is the subject of the last section.

Four techniques that forgive your mistakes

A bearing gets you close. It does not get you there. Each degree of error is 17 metres sideways per kilometre, and nobody holds a perfect line around fallen timber, through scrub and across gullies. Orienteers don’t try to. They plan each leg so that the country itself corrects them.

The four ideas below come from orienteering, where the target is a control, an orange and white flag at a mapped feature. They work just as well when the target is a campsite, a track junction or a water tank. The definitions follow Orienteering ACT’s skills lessons and Orienteering Ireland’s skills guide.

Handrails

A handrail is a line feature you can follow: a track, a fence, a creek, the edge of a forest. In the Australian bush add fire trails, ridgelines, spurs and powerline easements. While you are on a handrail you barely need to navigate, and you move at full speed.

The compass still has a job on a handrail. There are always more tracks on the ground than on the map, so at each junction check that the one you are taking runs in the direction the map says it should.

Catching features

A catching feature is something obvious beyond your target that tells you that you have gone too far: a road, a creek, a fence, the far side of a ridge. Before every leg, ask one question: if I miss, what stops me? When there is a good answer you can move quickly, because the worst case is a short walk back.

Orienteering ACT adds a warning: never head blindly for a catching feature. An overgrown track or a broken fence is easy to cross without noticing, and if you have drifted you may meet a different track from the one you expected. Keep checking the compass direction and the shape of the ground on the way. You will also hear the term collecting features for the things you tick off as you pass them: a creek crossing, a saddle, a fence corner. Each one confirms that you are still where you think you are.

Attack points

An attack point is a large, obvious feature close to a small, hard one. You go quickly to the attack point by whatever route is easiest, then slow right down and navigate carefully over the short distance that is left.

The reason is arithmetic. Five degrees of error over a kilometre is 87 metres, enough to miss a boulder completely. Five degrees over 150 metres is 13 metres, and you will probably see it. Orienteering ACT makes a further point: if a leg has no obvious attack point, treat that as a warning and take extra care all the way.

Aiming off

Aiming off is for a target that sits on a line feature running across your path: a footbridge on a creek, a gate in a fence, a track junction on a road. Aim straight at it and you will reach the creek, but if the bridge is not in front of you, you will not know whether to turn left or right. So aim to one side on purpose, far enough that your likely drift cannot put you on the other side. When you reach the creek, you know which way to turn.

Orienteering ACT’s example is a termite mound beside a watercourse: aim a little downstream of it, and when you reach the water you know to turn upstream.

Putting the four together

Good navigators string these into a plan before they take a step. A leg to a hut on a fire trail might go like this. Follow the spur down from the saddle (a handrail) to the creek junction at the bottom (an attack point). From there, take a bearing aimed a little left of the hut (aiming off). Walk it until you reach the fire trail (which is also the catching feature), turn right, and the hut is a few minutes along. At no point did the plan depend on walking a perfect line.

What throws a compass off

Metal and magnets nearby. A steel fence post, a car, a knife or a belt buckle will pull the needle while it is close. Step away and the needle recovers. Take bearings with the compass away from your body and well clear of anything steel.

Reversed polarity. This one is permanent. A strong enough magnet can remagnetise the needle the other way round, so that the red end points south. Nigel Williams of Glenmore Lodge, Scotland’s national outdoor training centre, had seen about thirty reversed compasses when he wrote about it, and knew of at least three mountain rescue call-outs for competent navigators carrying one. It can happen to any brand. His conclusion was that the usual culprit is anything with a speaker in it, including mobile phones and radios, along with the small magnets in some phone cases and in some gloves and buckles. Whether the phone is switched on makes no difference, because the magnet is in the speaker.

The habits that follow from that:

• Compass and phone in different pockets, and in different parts of the pack. The same goes for radios, cameras and GPS units.
• Check it before each trip against a second compass, or against the compass in a phone or watch. This is the best argument for owning a small backup.
• Hold it level. Even a correctly balanced needle will catch if the compass is tipped.
• If the needle and the country disagree, stop. Work out which one is wrong before you walk any further.

Common questions

Sources

All read on 2 October 2026.

• NOAA National Centers for Environmental Information, Geomagnetism frequently asked questions — what a compass lines up with, declination and inclination defined, which end of the needle dips in each hemisphere and where the counterweight goes, and that the field changes over time
• NOAA, Magnetic field calculators — the declination figures for Australian towns and cities (World Magnetic Model WMM-2025, calculated for 2 October 2026), their yearly change and their uncertainty
• Suunto, Understanding balancing zones — why needles are balanced, the two-zone system and the global needle
• Suunto, Understanding declination correction — fixed scales and adjustable declination
• Suunto, Understanding mirror compasses — sighting with the lid at about 45 degrees, and signalling
• Silva, How compasses work — the MN, ME and MS zones, what happens in the wrong zone, and that Silva’s site mainly sells MN
• Silva, Find your compass — baseplate, sighting and global-needle compasses, and the Field, Ranger and Expedition ranges
• Silva, How to navigate with a map and compass — the Silva 1-2-3 system
• Land Victoria, Map grids and magnetic information — Vicmap sheets are aligned to grid north and print the grid convergence and magnetic declination; the map scales published
• Melbourne Bushwalkers, Navigation Lessons (PDF) — the three norths, grid convergence in Victoria, “GrandMa’s Socks”, and the north-point diagram method
• Andrew Dawson, Unleashed Unlimited, Adjusting for the grid magnetic angle with a map and compass (3 March 2023) — the GMS and MGA rules, and what happens when the angle is negative
• Geoscience Australia, Map Reading Guide: How to Use Topographic Maps, edition 4 — the catalogue entry and free download, recommended as further reading
• Anthony Scott, Orienteering ACT, Lesson 8: Attack points, collecting features and aiming off (2020)
• Orienteering Ireland, Skills and techniques in orienteering — handrails, catching features, attack points, and the kinds of compass orienteers use
• Nigel Williams, Glenmore Lodge, Reverse polarity in compasses (revised July 2016)
• Darren Edwards, Trail Hiking Australia, What causes compass bubbles and how they impact navigation (updated 28 August 2026) — why bubbles form and when one matters
• Product details: Suunto, Clipper L/B SH; Silva, Pocket, Expedition and Expedition S; Mapworld, Pocket compass by Silva (the Magnetic South listing)

The distances quoted for bearing errors (17 metres per degree per kilometre, and so on) are our own arithmetic.