Once one of the prized treasures in the private art collection of the Ch'ienlung Emperor (r.1736-1795), the "Po-yuan Letter" by Wang Hsun now is in the Peking Palace Museum. This remains as the only surviving authentic example of signed Chin dynasty calligraphy. Appearing in the Ming dynasty (1368-1644), it has been admired ever since as a treasure from antiquity. However, Japanese scholars have considered it a rubbing copy. Many scholars have presented different opinions, but they all seem to lack evidence to support their reasoning. In other words, their conclusions are based on impressions of the work, and many of them merely follow previous opinions. Whether the work is authentic or not still remains an open question. The Japanese opinion stands out as unique, but it has not been met with much approval, mostly due to their lack of proof Other issues for study are the existence of the "Hsiian-ho mounting" during the Ming and Ch'ing dynasties and whether it was actually in the collection ofWu T'ing in the Ming. My approach starts with the letter itself and combines historical material and other examples of calligraphy as supporting evidence. I not only find evidence to determine its authenticity, but I also have resolved another problem by providing a detailed explanation for why scholars have not been able to find evidence for the "Hsuan-ho Mounting." The first reason is that previous scholars did not provide a general analysis of inscriptions and carvings, and the second is that many merely follow the opinions of the early Ch'ing connoisseurs Wu Ch'i-chen and Ku Fu without double-checking them. They did not realize, for example, that when Wu wrote about it being an "outline copy," he was already providing an important clue. In addition, Ku Fu mistakenly passed on incorrect evidence, due to his lack of expertise. Later scholars overlooked these followed them, thus magnifying a small oversight into a major error of judgement.