尺寸链的计算-tolerance stacking calculation

请教各位前辈，如下为一个计算累计公差的表格，本人有几点问题想请教，忘各位指点：
1、表格中的factor值是怎样算的？
2、为什么每行中σ 的计算方法为半公差限/6*factor值
3、上、下行数据链UDL\LDL的计算公式为何为mean值+/-6*sum的σ 值
4、 Above target以及 Below targe是怎样算的
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以上几点希望理解的前辈指导一下，thanks。

　 Design Target for Gap: 0.7 ± 0.30 Unit: mm Part
　 Before Coating Assemble
Upper Hinge Data from XXXXX
Item. Part Dimension Design (After thinking about the mean has 1.5σ shift)
Mean Tolerance Factor σ
1 Cavity Hinge upper A1: Rotaion hole to fixed plate 25 ± 0.150 1 0.0250
2 Front plate rivet C1: Front plate thickness 0.7 ± 0.020 1 0.0033
B1: Welding gap btwn front plate and hinge 0.3 ± 0.100 1 0.0167
3 Uper pivot alignment Door Hinge align hole 0 ± 0.050 0 0.0000
Cavity hinge align hole 0 ± 0.050 0 0.0000
D1: Assemble gap with Cavity hinge 0 ± 0.150 0.5 0.0125
E1: Assemble gap with Door hinge 0 ± 0.150 0.5 0.0125
4 Door Hinge upper F1: Rotation hole to base plate 1.2 ± 0.200 1 0.0333
5 Metal door G: Thickness of metal door 22 ± 0.200 1 0.0333
H1:Thickness of powder coating 0.1 ± 0.015 1 0.0025
　 Sum Mean= 0.7 σ= 0.0587
　 Min= 0.5238
　 Max= 0.8762
　 Range= 0.3523
　 Upper Cpk= 1.7029
　 Lower Cpk= 1.7029
　 Cpk= 1.7029
　 Cp = 1.7029
　
UDL = 1.0523
　 LDL = 0.3477
　 Out of spec PPM
　 Above target 153.9462
　 Below target 153.9462
　 Total rate out of limit 307.8923
　 PPT= 0.3079
A1=B1+C1+gap+H1+G1+F1+E1+D1