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The second part is based on the definition of the concept, focusing on some common research methods about how to measure the scale of the non observed economy.

第二部分在对未观测经济概念进行界定的基础上，着重介绍了几种常见的未观测经济规模的研究方法。

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The research focused on how humans navigate. Two common methods were analyzed.

该研究关注于人类是如何辨别方位。对两种常用的方法进行了分析。

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The Earth's rotation and revolution Movement was originally astrometry and ground studies of common research topics, but the methods and goals of different.

地球的自转运动和公转运动本来就是天体测量学和地学共同的研究课题，但方法和目的有所不同。