The sundial on abridged armilla 台中簡儀上的日晷

台中簡儀模型上有個日晷，若稍加分析，可確定它是工匠做錯了的。詳情請至http://blog.xuite.net/nycl.chiu/blog/27494787。

There is a gorgeous model of Jien-yi (simplified equiptment, 簡儀, abridged armilla) on display in the National Museum of Natural Science in Taichung, Taiwan. The model was made in China and the original one is still kept in ZiJinShan (紫金山), China. On the  lower level of the model, there a sundial on a horizontal plate. (See Fig. 1). This is not the same thing as what I saw in Beijing's museum where the plate is a ZhengFangAn (正方案, a square table used to find the precise north-south direction) with a long vertical needle seats at its center to cast shadow and then to find the true north direction together with the rings (up to 19 rings) on the its face. Now here on the model the rings were removed and replaced with hour lines of a sundial. The long needle is substituted with a regular gnomon, of course. However, the model maker left four mistakes on this dial: 1. The gnomon were misplaced; the lower tip of gnomon was not at the 'center' of the dial. (See Fig. 2). 2. The hour lines were not split into two groups to form two 'centers' to take care of the thickness of the gnomon. 3. The hour lines for time difference of 12 hours were not aligned. And 4. In between 1 a.m. and 2 a.m., were there only two lines. (See Fig. 3).