(20) N, .= -5d 4dx -3dx +3dx +4dx g+5dx 
2 X101" $55 192 103 105 10 107* ***198* 
*$dx] 99 4651117144 2° 0902107103 297104 197105” 
-3dy 196! ?dY 1 9g* *dY ; oog*5dy 1 9*4dy ; ,,*3dy, 1, 
(21) N, = -9dx, ?-16dx, 4725dx,94- 16dx, 9, -9dx -9dx, g-16dx, - 
0 0 106 0 09 
-25dx,,9-16dx,,,-9dx,,,t*l2dy,95*12dy,95,-12dy, 95 -l2dy, go* 
  
  
*12dy ,gg*12dy ,99- 12dy ,, ,- 12dy |, 
(22)  N, - -12dx,95-12dx, 94*12dx, 9, * 12dx 9, - 12dx | o5 - 12dx oF 
*tl2dx,,,t*l2dx,,,*25dy,g,tlódy,9,*9dy, 9, t9dy + 
+16dy, pgt25dy,07t16dy, pgt?dY, 0gt9dÿ,,1+16dy, 2 
The standard error of unit weight 
(23). 89 i7 dT 
The standard error of the standard error of unit weight 
  
(23a) 5, = 0, 16 sg 
The confidence limits are 
for the confidence level 5 per cent: 0.8 sg - 1.4 So 
for the confidence level 1 per cent: 0.7 89 - 1.6 So