The X-ray image principle and the mark ruler and standard sphere are introduced in this paper. The error from the mark ruler is also analyzed in the paper.

本文介绍了该系统的X射线成像原理、光路分析以及标尺和参考球的使用，并对标尺的固有误差作了分析。

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As a thunderstorm unleashes an early monsoon downpour, the brother suggests that a ruler's worth should be judged by a traditional standard.

ECONOMIST: A majestic moment for an ever more powerful ruler