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2.2 The Comparasion of the Capability of the Two Step 
  
Iterations 
Table 2 gives an example only observation 4 contained 
gross error which can not be located by first step but 
can be by second one. 
TABLE 2 ONE GROSS ERROR LOCATION BY TWO STEP ITERATIONS METHOD 
  
  
  
  
  
  
Point l1 2 3 4 5 6 7 8 9 10 | Noted in comprehehsive decision 
| RET Si .°. 54 2.5 . | error vector = E 
First litz6l .« |. T.T .. .- 8.5 3.0 . | gross error V,= 7 
Step | iso: . 9 .  . | point 4, 7 and 9 decided 
| | Pol . . | as Type À observation. 
| IMccvl .65 T8 81 | 
| fv. 1.2 1.2 . 2.3 —. | point 4, 7, 9 weighted zero 
jit=1l| $ | 4.1 -3.4 2.7 . | point 9 with good observation 
| IMcevi ‚29 35 .82 . | point 4, 7 need further detection 
Second ------------------7--7-7-7-7-7--7-7--7-7----- 
Step | EA 1.7 .8 2.3 . | point 4, 7 weighted zero 
|it=2| 8 | 5.8 -2.1 2.7 . | point 7 with good observation 
| IMcovi .30 .35 82 . | point 4 contained gross error 
| | v 1 5.3 .8 2.1 . | point 4 weighted zero 
litz3l 9 - | 8.1 -2.0 2.4 . | gross error complete reveal 
| IMccvl . .65 .35 82 . | in the residual 
Noted symbol in Table 2 and 4 : Noted in the comprehensive decisions : 
it = sequent number of the iteration, (1) The first step iterations, 
when it = 1, taking P = I it = 6 
V s standardized residual (2) The second step iterations, 
v = weighted zero residual when MCCV > 0.5, take 
ep = correlation coefficient of residuals critical value = 2.5 
MCCV = main component coefficient of v when 0.5 > MCCV > 0.3, take 
= the value is small nothing for decisions critical value = 1.5 
Table 3 gives examples about the differences of capacity 
of localizing two gross errors by two step iterations 
method. In comparision with the first step iterations, 
some mistakes decided in first step can be corrected in 
second one. 
TABLE 3 THE COMPARISION OF THE CAPACITY OF LOCATED GROSS 
ERRORS BY TWO METHODS 
  
  
  
Correlation | Two Gross errors | Two Gross errors 
coefficient | located by two steps | located by first step 
Ps = 0.88 | Viz 6, V,s-6 | point 5 correct 
| point 8, 9 wrong 
  
Pa = 0.88 | V,* -12, V,* -12 | point 7 correct 
| | point 4, 1 wrong 
  
Pu= 0.55 | 7, = -15, V,= 15 | point 1 correct 
| | point 6, 9 wrong 
  
Pr = -0.25 | Vis -8, V,= -8 | point 1 correct 
| point 8, 5, 9 wrong