天鈞 Tiānjūn, "Heaven's wheel,"is a potter's wheel. Compare Mozi 9.02: 子墨子言曰：「必立儀，言而毋儀，譬猶運鈞之上而立朝夕者也，是非利害之辨，不可得而明知也。 "You have to establish a standard. To speak without a standard is like trying to establish sunrise and sunset on a revolving potter's wheel." The contrast is between a potter's wheel, which turns (or we might say a weathervane) and something fixed, like a sundial. When a weathervane is lodged properly in its socket, it turns easily in any direction. The Mohists thought this was a paradigmatically wrong moral guidepost, but Zhuangzi is suggesting it is the right one. After all, a weathervane is responsive to its circumstances. What would be wrong would be to be a weathervane that wrote down is judgments and insisted on them, since whatever it says today it will likely contradict tomorrow. But is this a flaw? Would a weathervane be better if it resolutely pointed always in the same direction?
鈞 jūn and 均 jūn appear to be used interchangeably to mean "evenness," probably an extension from a primary meaning, "potter's wheel." 鈞 only appears in the phrase 天鈞 "potter's wheel of nature," in 2:06 and 8:06. 均 appears by itself as "evenness" in 3:01, 11:05, and 14:03, and in the phrase 天均, "potter's wheel of nature" again, in 8:11.