model are then measured in all grid points. From these figures a stand- 
ard altitude error is calculated and accepted as a measurement of the 
accuracy obtained. Unfortunately this figure is not a true standard 
error saying something about standard errors to be found in practical 
work, and the reasons for this are as follows. 
The residual y-parallaxes were not eliminated i. e. the grid model was 
not formed by relative orientation, 
'The test measurements were made for a single special plane, but in 
practice, models do not coinside with this plane, especially those of hilly 
terrain, 
'The test base used in some cases will give rise to an overlap less than 
50 %. 
From the above it is evident that the whole model volume ought to 
be more realistically tested, and standard errors calculated from such a 
test. 
[n short, the common procedure is: 
Simple measurements combined with trials to eliminate errors one 
after the other. Finally a great number of grid measurements used only 
to obtain standard errors. 
A much better method is to start with complete grid measurements, 
and from these calculate the required corrections at each adjustment 
point. After introducing these corrections it is sufficient to check in a 
limited way to ensure that no mistakes have occured. From the grid 
measurements, it is possible to calculate standard errors to be expected 
in the instrument after adjustment. 
Simple calculations, using the final check figures, will show whether 
the calculated accuracy has been obtained. 
The calculations involved in the method sketched are of considerable 
magnitude, and can therefore only be economically processed by means 
of an automatic computer. A program of these calculations has been 
designed to suit the Swedish electronic computer FACIT EDB in 
Stockholm. At present the program contains formulae for 17 adjust- 
ment points i. e. 17 unknown and their standard errors for the Wild 
A 7, but formulae for any instrument may be added without difficulty. 
Dy means of a set of parameters the program is prepared for any group 
of measured grid points. Experience will indicate the most favourable 
group of measurements. As well as for mechanical instrument correc- 
tion, the results may be used as mentioned in the first paragraph. It is 
also possible to solve the problem with arbitrarily chosen fixed adjust- 
ment points. This is convenient if some adjustment points are correct. 
After grid measurements the instrument is used in a normal way and 
corrections are made later when the results have been returned from the 
automatic computer, 
In [1] Hothmer has studied the effect of errors in gimbal axes but 
according to this report the results were inconclusive. His investigation 
3