22 
The relations between dx, and dx, on one hand and the image coordi- 
nates on the other hand are as follows 
dz’ = — y' dx dz’ = —3"dx, 
dy = du dy’ = x de, 
Since small values of the rotations are assumed we can use the follow- 
ing relations 
Consequently 
de’ = — y' dx, dx” = — y'dx, 
dy =z" d=, dy" — (x' — b') dx, 
Substituting these relations into (3) and (4) we find after some computa- 
tions 
da x! ha : ; | x’ (x € b!) 
S ogy (tx I T) dos d) — y de dy (04) 
dà x? + y”? 
+ m D. Q (do, — dx) + (2 x' — b') dx, (65) 
These expressions can be somewhat simplified after substitution of 
(63). 
The accuracy of the corrected coordinates with respect to the y- 
parallax measurements can be found from the usual error propagation 
procedures applied to the expressions (64) and (65). 
We will here demonstrate the determination of the accuracy for 
certain points only. 
We regard the points 
v o, v dy, a = 0, %, ='0); a, = b', x = b' 
, , , , , , , , , , 
yi 7 0, 94 7 0, Ya = b, y — — o; y = du = —b