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According to Fig.l the differential formulae are 
dx 
- dx, + xdm_ + y(da + dB) (3) 
Bye Tay, > ydm, - xda (4) 
Consequently six unknowns are to be determined. Measurements in at 
least three points are consequently required. Obviously more unknowns 
can be introduced if corresponding regular errors are to be expected. 
1.2 Correction equations and working correction equations. 
The correction equations are derived from the error equations (3) - (4) by 
changing the signs. For redundant measurements the corresponding work- 
ing correction equations are 
V 
x 
dx, - xdm. - y(da + dB) - dx (5) 
Il 
V 
y dy, = ydm,, + xda - dy (6) 
After measurements in n points the normal equations can immediately be 
formed from expressions (5) - (6). Evidently it must be advantageous to 
choose the points in such positions that the point of gravity coincides with 
the origin of the coordinate system x, y. The sum of the x- and the y-coor- 
dinates will then be zero and the normal equations will be considerably sim- 
plified. 
We assume 25 points to be chosen according to Fig. 2. 
The working correction equations applied to the 25 points are demonstrated 
in Table 1.