11 
Because the tolerance was exceeded in more than five percent of the tests, 
an investigation was made of the possible reason for this fact. It was found 
that the upper rod of the mechanical projection system was deformed, probably 
due to aging of the material. The rod was sent to the manufacturer for adjust 
ment, then after restoration, test measurements and computations showed 
that the original quality of the instrument was attained. On 10 April and 9 
September 1963, for instance, the standard error of unit weight was found to 
be 4.3 microns. Later tests indicate that this quality is still being maintained. 1 
Moreover see Diagram 1. 
Image Coordinates in Aerial Photographs. 
Comprehensive tests of aerial photographs have been made according to 
procedures used in Hallert 1960 b. Five aerial cameras (Aviogon 6", 9"x9", 
film) have been used for photography of the Óland test field from various alti 
tudes, primarily 1200 meters. From tests during the spring and summer 1963 
the standard error of unit weight of the image coordinates was determined for 
circles with varying radii. The general expression for the standard error of 
unit weight was determined as follows: 
só = 4.i-0.oi7ir , + 0.ooo576r' 2 
Histogram and normal distribution curve of 
the residuals after adjustment in nine points 
Autograph A7-310 
Left projector, base: zero 
Operator 1 
Number September 1963 
of residuals 
Diagram 1. Normal distribution test of image coordinate residuals. Grid method. Auto 
graph A7. chi 2 = 15.51 chij iagr = 7.93. The normal distribution hypothesis is accepted. 
J ) It is always advisable to perform the tests in different enlargements and different orien 
tations of the grid.