如果一个交互式计算机屏幕要在实用性上与白板相匹配，它必须在手臂长度范围和横跨房间范围内是可视的。

If an interactive computer screen is to match a whiteboard in usefulness, it must be viewable from arm's length as well as from across a room.

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这是另一个朋友的手臂长度，两只手臂的长度。

This is another friend arm length, two arms lengths.

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你与来自前后的朋友们都有相同的手臂长度距离。

You have the same arm length from the friends in front and back of you.

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