Compass Correction Calculator
Convert true, magnetic, and compass bearings with declination, deviation, epoch drift, and heading error drift checks.
🧭Quick Navigation Presets
⚙Bearing Inputs
📊Correction Constants
📘Reference Tables
| Declination Band | Magnitude (deg) | Map Label | Field Priority |
|---|---|---|---|
| Low | 0-3 | Minor correction | Update yearly |
| Moderate | 4-10 | Standard correction | Check each trip |
| High | 11-18 | Critical correction | Check every leg |
| Very High | 19+ | High-risk error | Use dual checks |
| Heading Error | Drift at 1 km | Drift at 3 km | Drift at 5 km |
|---|---|---|---|
| 1 deg | 17 m | 52 m | 87 m |
| 2 deg | 35 m | 105 m | 175 m |
| 3 deg | 52 m | 157 m | 262 m |
| 5 deg | 87 m | 262 m | 437 m |
| Given Bearing | Declination | Deviation | Compass Output |
|---|---|---|---|
| 100T | 8E | 1W | 093C |
| 145T | 11W | 2E | 154C |
| 280T | 4E | 0 | 276C |
| 012T | 7W | 2W | 021C |
| Epoch Age | Shift Rate | Total Shift | Action |
|---|---|---|---|
| 0-2 years | 4 min/yr | 0.13 deg | Normal update |
| 3-5 years | 6 min/yr | 0.50 deg | Apply correction |
| 6-10 years | 8 min/yr | 1.33 deg | High priority |
| 10+ years | 10 min/yr | 1.67+ deg | Re-validate map |
Correcting a compass is a needed part of navigation. You call correction the change of magnetic direction to true north. The opposite operate uncorrection.
You need to correct the reading of a compass for two separate effects. Magnetic declination, or variation, is the first: it shows the angle difference between true and magnetic north. Magnetic north points the local direction of Earth’s magnetic field.
How to Correct a Compass
Because of motion of the magnetic pole, corrections adjust each year. The second effect calls deviation.
Deviation of a compass depend on the ship. For instance, a compass can well show north, but read wrong in 50 grades, when the ship points west. Here do not deal about damage of the compass itself.
Some devices, as a compass assembled on plastic control panel, move because of magnetic impact of a wheel inside the panel. Also other things create problems. A magnetic case can divert the compass direction.
Magnets in a stereo unit can push it swing in 30 grades. Nearby metal or fields in a motorhome also require calibrating to correct the compass. Even a liquid compass require calibrating against those nearby fields.
For find true north by means of a magnetic compass, you must know its errors. Those usually are listed on a card according to particular angles. Deviant card commonly happens in 15- or 30-degree interavls.
You require also current chart of magnetic declination. It points the apt correction for your area. At compasses with adjustable declination, as Suunto M-3, Silva Expedition or Brunton TruArc, you simply turn it.
Enclose the provided metal key in the adjusting screw. Turn it, until the measure show the right grade east or west of 0. That built-in correction helps, because magnetic north depends on your position.
Some use cheap oil-filled compass without adjustment and simply correct as they go.
