请问StDev(within)的计算公式是什么

请问StDev(within)的计算公式是什么

样本 X1 X2 X3 X4 X5
1 99.70 98.72 100.24 101.28 101.20
2 99.32 100.97 100.87 99.24 98.21
3 99.89 99.83 101.48 99.56 100.90
4 99.15 99.71 99.17 99.30 98.80
5 99.66 100.80 101.06 101.16 100.45
6 97.74 98.82 99.24 98.64 98.73
7 101.18 100.24 99.62 99.33 99.91
8 101.54 100.96 100.62 100.67 100.49
9 101.49 100.67 99.36 100.38 102.10
10 97.16 98.26 97.59 100.09 99.78

StDev(Overall)=1.124835 我推出来了
StDev(within) 0.870623 怎么都算不出来。请高手指教，希望能详细点，我是新手！

谢谢！