With direction index, sapphire cover lens, never abrasion.
带有方向标，蓝宝石镜头，永不磨损。
The index of refraction for the extraordinary ray is therefore a function of direction.
折射光线的折射率因此在各个方向不同。
The direction finding is an important index of electronic reconnaissance.
测向则是电子侦察的一个重要指标。
The direction finding is an important index of electronic reconnaissance.
测向则是电子侦察的一个重要指标。
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