Three independent calibrations.
Each sensor is calibrated on its own — don't confuse them. The magnetometer keeps heading honest, the accelerometer keeps bank true, and a short gyro alignment removes drift at power-up.
| Magnetometer | hard- / soft-iron fit — heading |
|---|---|
| Accelerometer | 6-face offset & scale — bank/pitch |
| Gyro | static "Align" window — drift |
Heading that stays honest.
Metal and avionics distort the local magnetic field (hard- and soft-iron effects). Calibration maps that distortion and corrects it, so magnetic heading reads true in the installed environment — not just on the bench.
Rotate
Turn the unit through a range of orientations so it can sample the field from many directions.
Fit
A 3D fit (or 2D when motion is limited) recovers the hard- and soft-iron correction.
Apply
The correction is stored and applied continuously to incoming magnetometer data.
The 6-face procedure.
A small per-axis offset or scale error tilts the measured gravity vector and shows up as a bank error that grows toward 45°. A classic six-point fit removes it. Hold the unit still on each of its six faces in turn:
Face +X up
Hold steady until the sample is captured.
Face −X up
Flip to the opposite face, hold still.
Face +Y up
Rotate to the next axis, hold still.
Face −Y up
Opposite face, hold still.
Face +Z up
Level, hold still.
Face −Z up
Inverted, hold still.
The fit recovers a per-axis offset + scale, applied to the raw accelerometer before the attitude filters — so every estimator benefits.
A few seconds, on the ground.
Every gyro has a small zero-rate bias that, left uncorrected, would drift the heading and attitude. A short static "Align" window at power-up — held still on the ground — measures and removes it automatically.
| When | at power-up, on the ground |
|---|---|
| Condition | aircraft held still |
| Window | a few seconds, automatic |
| Result | zero-rate bias removed |
Calibrated once, trustworthy after.
With the three calibrations done, every attitude estimator starts from clean data.