In the lower volume twenty, the Earth Plate should be substantial, and the Heaven Plate should be empty.

地以八方正位，定坤道之輿圖，故以正子午為地盤，居內以應地之實；天以十二分野，正躔度之次舍，故以壬子丙午為天盤，居外以應天之虛。

The earth uses the eight cardinal directions to define the map of the坤 (Earth) path, so it uses the correct Zi and Wu directions as the "Earth Plate," located in the inner layer of the compass, to correspond to the earth's "substance." The heavens use the twelve regions to correct the movement of celestial bodies, so it uses the area between Renzi and Bingwu as the "Heaven Plate," located in the outer layer of the compass, to correspond to the heavens' "emptiness." Since earthly energy is still, seeking dragons and capturing pulses should use the Earth Plate; since heavenly energy is dynamic, receiving water and establishing directions should use the Heaven Plate. This is the fundamental principle behind the use of the true needle and the interwoven needle on the compass.

今人論針，乃有正針逢針之分，且有彼是此非，又有專用此而不用彼者，蓋不知二針各有取義，相為用而不相為悼耳。地盤何取於正子午也？原地盤分屬，以八分為分屬。一從《河》《洛》中來，《河圖》之象，列以八方，《洛書》之數，亦有四正四隅，舍此之外，則無理氣。經之所謂氣從八方，混元子所謂八定位，《靈轄經》所謂內立八極以統八方之氣是也。

Nowadays, when people talk about the needle in the Luo Pan, they distinguish between "Zheng Zhen" and "Feng Zhen," and each side insists on their own view, even to the point of using one exclusively and rejecting the other. This is because they do not understand that the two needles each have their own meaning and are meant to complement each other rather than interfere with one another. Why does the Earth Plate use the "Zheng Zi Wu" (True Meridian)? Originally, the Earth Plate is divided according to the eight directions, and everything comes from the "He Tu" and "Luoshu": the "He Tu" arranges the eight directions, and the "Luoshu" has four cardinal and four intercardinal directions. Outside of these, there is no rationality or qi flow. The classic text says "qi comes from the eight directions," and Huyuanzi says "eight fixed positions," while the "Lingxia Jing" says "establishing the eight extremes within to unify the qi of the eight directions." All of these refer to this principle. The Earth Plate uses the "Zheng Zi Wu" precisely because the qi of the eight directions originates from this central line.

夫既以八方分位，則壬子癸共一坎也，丙午丁共一離也，一卦三山，其以正子午為地之中，夫何疑乎！古人用以測地，正為氣從八方，故以正子午之針打龍，所謂龍從地下求者，指地盤言也。夫地氣何以分貴賤？乃從天星也。天之躔度以十二次舍為分，壬子共一子也，保以辨之？

Since the eight directions are used to divide the positions, the heavenly stems Ren, Zi, and Gui all belong to the same Kan trigram, while the heavenly stems Bing, Wu, and Ding all belong to the same Li trigram, with one trigram governing three mountains. Taking the true Zi-Wu line as the central axis of the Earth, what is there to doubt? The ancients used it to measure the land, precisely because the qi comes from the eight directions. Therefore, using the true Zi-Wu needle to control the dragon, as said "the dragon is sought from beneath the earth," refers to the Earth Plate. Then, by what standard is the Earth qi divided into high and low? It is based on the heavenly stars. The celestial degrees are divided into twelve sections, and since Ren and Zi both belong to the Zi position, by what means can they be distinguished?

凡次舍十二，每次分得三十度，合考之，玄枵次舍自女八度起至危十五度方成三十度，夫女四星十一度半屬癸，今玄梧起於女八度，是僅侵癸之三度而已；虛二星九度半屬坎，危三星十八度屬壬，今玄根止於危十五度，亦僅成剩壬之三度而已，則玄枵子分，豈非壬子之間乎？故以壬子之間為天盤之子，又復何疑。即子而推丙午，亦共一午，則壬子丙午之間，正為天之中矣。

Each of the twelve mansions is divided into thirty degrees. When considered altogether: the mansion of Xuanxiao begins at eight degrees of Nu Xiu and reaches fifteen degrees of Wei Xiu to complete thirty degrees. Nu Xiu has four stars covering eleven and a half degrees, belonging to Gui. Since Xuanxiao starts at eight degrees of Nu Xiu, it only intrudes into Gui by three degrees. The two stars of Xu Xiu cover nine and a half degrees belonging to Kan, and the three stars of Wei Xiu cover eighteen degrees belonging to Ren. Since Xuanxiao ends at fifteen degrees of Wei Xiu, there remains three degrees of Ren. Therefore, the portion of Xuanxiao that governs Zi is not in the middle of Ren and Zi, but between them. So taking Ren Zi as the Zi position of the Heaven Plate, is there anything to question? By extending from Zi to Bing Wu, they are all part of the same Wu position. Therefore, the area between Ren Zi and Bing Wu is the central line of Heaven. The reason the Heaven Plate is offset by half a position from the Earth Plate is because the division of the twelve mansions and the twenty-four mountains are not consistent.

古人向從天中立，正以應天之虛，從天盤也。蓋地氣靜，故尋龍捉脈當從地盤之靜定為主；天氣動，故收水立向當以天盤之旋動為主。且貴賤在天星，若不從天盤而定，則天星無據，將何以發用乎？是故收生旺之氣於坐下，而又迎吉曜之氣於向方，則天與地通，而動與靜合，斯可以召福而迎祥也。然則正針逢針，豈有偏重偏用之理，但龍是一定之龍，向無一定之向，縱龍脈有挨加，亦是因方而有挨加。昔人云：立穴易，立向難。正以動體之難捉摸耳。夫所謂神而明之，存乎其人者，其在天盤乎！

Ancient geomancers established directions based on the central line of the Heaven Plate, precisely to respond to the "void" of Heaven, using the Heaven Plate. Since the earth energy is still, seeking the dragon and capturing the pulse should primarily rely on the stillness of the Earth Plate; since the weather is dynamic, receiving water and establishing directions should primarily depend on the movement of the Heaven Plate. Moreover, the distinction of wealth and poverty depends on the heavenly stars; if not determined by the Heaven Plate, the heavenly stars would have no basis and would have no way to function. Therefore, in the sitting position, one gathers the vital energy of life and prosperity, and in the direction, one welcomes the auspicious stars. In this way, Heaven and Earth connect, and movement and stillness harmonize, thus summoning blessings and auspiciousness. If this is the case, how can the true needle and the interwoven needle have any particular emphasis or exclusive use? The dragon is fixed, but the direction is not fixed; even if there are additions along the dragon line, they are due to the directional positions. The ancients said, "Establishing a site is easy, establishing a direction is difficult," precisely because things that are dynamic are hard to grasp. What is meant by "to grasp the subtle and make it clear lies in the person himself" is probably the effort made on the Heaven Plate. In summary, the dragon is still and the direction is dynamic; the Earth Plate determines the stillness, and the Heaven Plate responds to the movement. The principles of reasoning and energy flow are thus fully connected here.