iOS sensor inventory

Refresh rate: 10 Hz for 60 s – keep the device steady or shake it, and watch the console.

What you just saw

• acceleration is already gravity-compensated (if available). When the sensor cannot remove gravity, only the accelerationIncludingGravity key shows up—and the spec tells you what you must expect.
• rotationRate (alpha,beta,gamma^°/s) maps directly to the gyro reading.
• webkitCompassHeading comes from fusion of the magnetometer and optionally the gyro; resolution depends on calibration status. If you need raw mag, DeviceMotionEvent.magnetometer is missing on iOS.
• Refresh interval on current iPhones is ~62.5 Hz (16 ms). It drops to 30 Hz with power-saving enabled.

HPR take-aways for your project

Heading ≈ webkitCompassHeading
Pitch = - e.beta  (degrees, device-orientation event)
Roll  = - e.gamma
Heave/vertical acceleration = e.acceleration.z when phone is mounted vertical, bow forward.

Need raw magnetometer? At the moment iOS only exposes the fused heading, not μT components. You could obtain them with a native Swift app instead: CMMotionManager.magnetometerData.