关于粗糙度的一些问题，望各位大大能帮小弟解决

不知道有无大哥对德国DIN标准有了解，小弟最近得到一份图档，其粗糙度标注为：
Rmax20以及Rmax20*，一些相关资料如下：
the surface roughness can max. Ra=20 (acc. to DIN ISO 1302), material separating is allowed
the note means: in a total length of ...mm You measure x segments with a segment length of ... mm
==> ** measurement length is 4.0mm, measurement segment is 0.8, count of segments is 4
==> *** measurement length is 4.0mm, measurement segment is 0.8, count of segments is 3
希望有人能帮助小弟搞清楚图纸要求的粗糙度到底是多少，用国内一般使用的表示方法应该是Ra3.2，Ra1.6，Ra0.4等等...感激不尽