True North vs Magnetic North
A compass needle follows Earth's magnetic field, which converges on the magnetic pole — currently in the Arctic Ocean and drifting, not at the geographic North Pole. The angle between the two, called declination, ranges from 0° to over 20° depending on where you stand, and our compass corrects for it automatically.
Two norths (plus a third for map nerds)
True north is the direction to the geographic North Pole — the point where Earth's rotation axis meets the surface, and the north that maps, coordinates and navigation are built on. Magnetic north is where a free-spinning needle actually points: the spot where the planet's magnetic field lines plunge vertically. They're over 400 km apart. (Paper-map users meet a third, grid north — the direction of the map grid's vertical lines — but for everyday use the first two are the story.)
Why the needle lies, and why the lie keeps changing
Earth's field is generated by churning molten iron in the outer core — a moving, messy dynamo, not a neat bar magnet. So the magnetic pole wanders: through the 1900s it crawled a few kilometers a year across Arctic Canada, then sped up dramatically toward Siberia around the 2000s, forcing extra updates to the World Magnetic Model that navigation systems rely on. The practical consequence is that declination is a function of place and date: the correction that's right in Mumbai is wrong in London, and the correction that was right a decade ago has drifted since.
How big is the error where you are?
Along a wandering line through the Americas and another through Asia (the agonic lines), declination is zero and a compass is accidentally honest. Most of India sits near 0–2° W — small. Western Europe runs a few degrees; the eastern US around 10–15° W; parts of Alaska and New Zealand exceed 15–20°; and near the poles the concept nearly breaks down. As a feel for scale: walking 1 km on a bearing that's 10° off puts you ~175 m from your target — irrelevant on a stroll, decisive in fog, at sea, or over long distances.
What phones and this site do about it
Your phone's magnetometer reads magnetic heading; software adds the declination for your location to display true heading. Our online compass and qibla finder do exactly this — the correction is computed from your coordinates, which is why they ask for location, and the qibla bearing especially benefits because a few degrees matter over 5,000 km. The figure-8 calibration dance phones request isn't superstition: it lets the sensor separate Earth's field from the magnets in your case, car mount and headphones. If the needle spins or sticks, calibrate, and step away from metal.
When you should care
Ignore declination when following a phone's corrected arrow — it's already handled. Care when mixing tools: taking a bearing from a paper map (true/grid north) and walking it with a raw magnetic compass needs the local declination added or subtracted — the value is printed in the map margin, with the year, precisely because it drifts. And if two compasses disagree, check the date of whatever correction each is using before blaming the hardware. For a hands-on feel, our compass how-to walks through headings, bearings and the Focus mode.