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# xTrueNorthZVertical

A reference frame where the Z axis is vertical and the X axis points to the geographic north pole.

```
static var xTrueNorthZVertical: CMAttitudeReferenceFrame { get }
```

## Discussion

Use this option to determine the attitude of the device relative to true north. For example, you might use this to implement more precise navigation. The [`yaw`](/documentation/CoreMotion/CMAttitude/yaw) (Z-axis) value in [`CMAttitude`](/documentation/CoreMotion/CMAttitude) is `0` when the X axis is aligned with true north.

The device must have a magnetometer and that sensor must be available. Location services must also be available to calculate the difference between magnetic and true north. If the magnetometer isn’t currently calibrated, Core Motion prompts the person to move the device to calibrate it.

---

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