X-BAR实例，请解！

数据如下
4.00%
3.84%
4.24%
3.45%
4.62%
2.91%
3.90%
4.13%
2.91%
4.14%
4.12%
2.61%
3.16%
3.06%
3.59%
2.34%
1.93%
1.59%
2.23%
3.32%
2.66%
2.41%
2.17%
2.03%
2.12%
1.72%
2.05%
2.01%
2.21%
4.72%
1.41%
1.84%
1.91%
2.12%
2.86%
2.80%
2.25%
2.26%
2.06%
1.63%
2.22%
1.61%
1.87%
1.65%
1.70%
2.28%
1.81%
2.06%
1.74%
1.82%
1.54%
1.68%
1.87%
1.21%
1.88%
1.34%
1.91%
1.61%
1.99%
1.91%
2.20%
1.97%
X-BAR图计算控制上限为3.6％，计算标准差为0.89％，均值为2.44％
控制线原理为过程均值±3倍标准差，为什么控制上限不能用2.44+3*0.89计算。
另外，不良率警戒线是否应为X-BAR图控制上限.
请各位大师帮忙，谢谢！