Georges Renault DELTA4000 Manual Operario página 23

3) Calculation of W:
2 2
W = b S
There is a 5% probability of not having a normal distribution if W is lower than W95 given in table C:
Table C :
N W95
15 0.881
20 0.905
25 0.918
30 0.927
35 0.934
40 0.940
45 0.945
50 0.947
5 - NORMAL DISTRIBUTION TEST: POPULATION OVER 50 MEASUREMENTS (CHI-SQUARED
TEST)
1) Distribute into classes of at least 4 or 5 measurements
2) Calculate the mean and standard deviation
mean:
∑
x
i
=
X ---------- -
N
standard deviation:
2
∑
( )
x – X
i
σ
= --------------------------- -
N 1 –
3) Calculate for each class limit li:
( )
l – X
i
u = ---------------- -
i σ
4) Calculate:
2
( ' )
n – n
2
i i
∑
χ
=
----------------------- -
'
n
i
where:
n = number of measurements in class i
n' = theoretical number of measurements for a normal distribution
' [ ( ) F u (
n = N F u –
i i i 1 –
DELTA4000/5000/4D/5D
) ]
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