sure- 
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ig 
Mw 
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January 1960 
The standard error of unit weight is 
Summary 
From measurements of image coordinates and parallaxes in grids of high 
and known precision and treatment of the results as demonstrated above, 
unique and reliable information can be obtained concerning the accuracy of 
the measurements in the instrument. Simultaneously some systematic 
errors (adjustment data) of the instrument are determined according to 
the method of least squares. 
Necessary data for the determination of the accuracy of arbitrary functions 
of the measurements are also determined and demonstrated. 
Using the same grids or grids of equal quality different instruments can be 
compared concerning the accuracy of some fundamental operations in the 
demonstrated manner. 
More parameters can of course be introduced in the adjustment for a de- 
termination of possible systematic errors. As long as the square sum 
[vv] decreases significantly the introduction of the additional parameter is 
justified. 
When the standard error of unit weight approaches the setting standard 
error (the standard deviation of individual settings) of the coordinate or 
parallax measurements as determined from repeated settings only, the 
systematic errors are evidently very well determined. It is, however, 
always most important to remember that systematic errors sometimes 
can be correlated and that they can consequently substitute each other more 
or less completely. If, for instance, the glass grid is affected by an un- 
known affine deformation, this systematic error can be referred to the 
stereocomparator through the adjustment procedure. 
For the determination of tolerances for residuals in individual points the 
principles of confidence intervals for certain confidence levels are very 
suitable.