位置度的标注

标在位置度的公差后面，是一个圆圈包含的S，就象圆圈包含的M代表最大实体，圆圈包含的L代表最小实体，请问高手这个S代表什么意思。急盼回复！ [s:10]

中国标准中无S加一圆圈的标注方法。我在国外的资料上找到相关内容，其中“Where the modifier symbol       ”后面跟的就是S加一圆圈的符号，我无法复制上来。我看应可理解为独立原则。

以下是摘录的英文资料：
6.1 Regardless of Feature Size(RFS)- Referencing a datum feature on an RFS basis means that a centering about its axis or center plane is necessary, regardless of the actual size of the feature. Where a geometric tolerance is applied on an RFS basis, the specified tolerance is independent of the size of the considered feature. The tolerance is limited to the specified value regardless of the actual size of the feature.
6.1.1 Where the modifier symbol       is specified with the datum reference, the datum feature
size variation does not allow increased tolerance.
6.1.2 Where the modifier symbol       is specified with the tolerance, the controlled feature size
variation does not allow increased tolerance.
6.1.3 Where the modifier symbol       is specified with both the datum reference and the
tolerance, the tolerance applies with no increase.

哪个国家的图纸啊？

英文的，有中文吗！