CPK问题，请高手帮忙分析

4.780 4.770 4.770 4.770 4.770
4.770 4.770 4.760 4.760 4.760
4.770 4.780 4.780 4.780 4.780
4.780 4.780 4.770 4.770 4.770
4.790 4.790 4.790 4.790 4.780
4.780 4.780 4.780 4.790 4.780
4.770 4.770 4.770 4.770 4.770
4.770 4.770 4.760 4.770 4.760
4.760 4.760 4.750 4.750 4.750
4.780 4.780 4.780 4.780 4.770
4.770 4.780 4.770 4.770 4.770
4.780 4.780 4.780 4.780 4.780
4.780 4.770 4.770 4.770 4.770
4.770 4.760 4.760 4.760 4.770
4.770 4.770 4.770 4.770 4.770
4.770 4.760 4.760 4.760 4.760
4.780 4.780 4.780 4.780 4.780
4.770 4.770 4.780 4.770 4.770
4.770 4.760 4.760 4.760 4.760
4.770 4.780 4.770 4.770 4.770
4.790 4.790 4.780 4.790 4.780
4.780 4.770 4.770 4.780 4.770
4.760 4.760 4.760 4.760 4.760
4.790 4.790 4.790 4.790 4.780
4.780 4.780 4.780 4.780 4.780
数据如上，25组，每组5个数据，标准4.80+0/-0.05（也就是只有下公差），
用MINITAB计算CPK值，结果为2.33（太好),但做X-R图时，10多个点超出控制线。
不太明白为什么多点超出控制线而CPK值却很好，请各位高手帮忙分析.l