1 Fèn. A modular unit of length. It has eight possible grades or values ranging from 0.60 to 0.30 cun, or from about 19.2 to 9.6 mm. Its absolute value in any given building depends on the rank of that building. For our purposes, this is the more important of the two terms; this is the one we mean when we write fen without a tone mark.
2 Fen. (Technical limitations prevent us from showing the macron above the e.) An absolute unit of length, equal to 0.01 chi or 0.1 cun or about 3.2 mm. We use chi or cun as the absolute units of length, which allows us to avoid the confusing use of fen.