16 
A common value for the standard error of unit weight of the measurements 
with an Ultropak microscope device is 2.5 microns, provided that three repli 
cated settings are made in each point and that the average is used. 
This means that the elevation differences of the surface from a plane through 
three points must exceed +7 microns in order to be regarded as significant. 
An example of flatness test is shown in Diagram 2. 
The Relative Orientation. 
The elements of the relative orientation and the residual j-parallaxes are, 
among other data, linear functions of the observed ^-parallaxes in the orien- 
Flatness 
of the glassgrid nr 410 (9"x9") 
©0 
0 -1 
O +1 
O ♦ 1 
O ♦ 2 
O -1 
O -3 
O -3 
0 -i 
0 * 1 
0-5 
0-2 
O -1 
0-5 
© o 
0-3 
O ♦ 1 
o -4 
o o 
O -3 
©0 0-3 0 -1 0*1 0-2 
Absolute orientation with the aid of the three 
indicated points. The grid supported bya 
surface plate. 
s 0 = 1,9 microns 
M = 2,3 —*— (theoretically 2,5>im) 
The confidence limit of individual residuals on 
the five per cent level ± 6,3 microns. 
Diagram 2. Residual elevation errors in the glassgrid with respect to a plane through the 
three indicated points.