characteristic spot heights (a totalof 15 000 points). Two 
contour sheets at the scale 1:2 500 basedon two independent 
profiling operations were submitted (Fig. 6). 
Zeiss GZ-1:  Contours at the scaleof 1:3 000 plotted off-line by the Zeiss 
Electronic Contourliner. These contours were based on 
graphically recorded profiles at a profile interval of AX = 
8 mm (Fig. 7). 
Zeiss Jena Orograph: VEB Carl Zeiss Jena provided the Working Group with 
a contour sheet at the scale of 1:2 500 which was manually 
compiled fromdrop lines. The interval of the profiles used 
for this map is AX = 4 mm (Fig. 8). 
The accuracy of the above contours was determined using the A7 
stereomodel in a similar way as when testing the accuracy of the basic 
profile data. The contour sheets were oriented on the A7 plotting table to 
correlate the contour information with the stereomodel. After correcting 
the contour data fora possible systematic vertical shift, standard errors 
were calculated from the differences between the contour heights and the A7 
readings. These standard errors were reduced for the effect of the estimated 
standard error in the checking procedure. The results are listed for 
different slope angles in Table VIT. 
In order to provide a comparison of the above resultswith contours 
plotted ona conventional photogrammetric plotter,a 1:2 500 scale contour 
map (2.5 m contour interval) of the Ripon test area, compiled on the A7, was 
evaluated (Fig. 2). The same technique was used for comparing the contour 
heights with the terrain heights, measured in the A7 stereoscopic model. 
The standard height errors, calculated for these contours for the different 
slope angles have been included in Table VII. 
It is interesting to compare accuracies listed in Table VII with 
the standards currently used in some countries. We selected for this purpose 
tolerances for the German Base Map at the scaleof 1:5 000, which one may 
consider as typical of an advanced and densely populated country.