铜钱正背面的阴阳原理
铜钱设有两面，有字和无字。所以有“字面”和“背面”。认人看正面，认钱也看有字的一面。所以古代一致上认同有字的一面为正面，无字的一面为背面。这就确定了正面（字面）和背面了。
天为阳而地为阴。世上的生物都是背朝天而面朝地。这就是原理所在。铜钱的背面就确定为阳而字面就确定为阴。一切事物皆法於天地。
尤于现代各国的钱币设计不同，很多钱币不再真正的把钱币的一面设定为字面。所以我建议大家起卦时还是用铜钱或有清楚分辨字面和背面的钱币为佳。
应用的铜钱或钱币也以同一个朝代或政府为佳。我不建议用大变动中发行的钱币。
The Yin Yang Determination of Two Sides of Copper Coin
Copper coins have two sides, with and without words. So there are “Front Side” and “Back Side“. We know a person by the face and we read a coin by its words. Therefore, in ancient times, it was agreed that the side with words was the “Front Side”, and the side without words was the “Back Side”.
The Heaven is yang and the Earth is yin. The world creatures’ back is facing the heaven and the face is facing the ground. The “Back Side” of the coin is identified as yang and “Front Side” of the coin is identified as yin. That’s the rule of law.
However, the design of coins in modern countries is different. Many coins don’t really set the coin with one side to show the words. Therefore, I suggest that when you get a Gua, it is better to use copper coins or modern coins that clearly distinguish between the “Front Side“ （with wordings) and the “Back Side” (without wordings).
The copper coins or coins used are preferably from the same dynasty or government. I don’t recommend using coins circulated during the era with massive change.