Orientation sensor and mouth IR detector.

方向感应能力和嘴内有红外线感应器。

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The orientation is determined by the device orientation sensor.

显示的方向是由设备的方向传感器来决定的。

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User orientation sensor: directional heading from a digital compass.

方向感知：基于数码罗盘的方向指南。

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One problem that was evident in the first generation Kindle DX persists in this model: the orientation sensor is a bit nuts.

ENGADGET: Amazon Kindle DX Graphite review

The orientation sensor automatically adjusts between portrait and landscape mode in most applications when the device is tilted, and the 2-Axis Accelerometer is great for controlling games that need simultaneous steering and acceleration.

ENGADGET: Pandigital Supernova available mid-October for $230, is an eReader in Android tablet disguise

Now, you can lock the orientation sensor and pretty much never encounter this issue again (we can't ever really imagine needing to read a text-based book with adjustable font sizes in landscape mode, after all), but it seemed worth mentioning given it goes unchanged since the previous version.

ENGADGET: Amazon Kindle DX Graphite review