This report presents the analysis of 47,000 of the settings made by thirty of the observers after their training and practice sessions, using seventeen different viewing conditions.nThe targets used in the comparison of conditions were six miniature tents photographed against a model of hilly terrain and oriented such that their ridges were in the direction of flight. Ten settings were made on each target in random order by each observer for every viewing condition. The standard deviations for the individual targets were computed and averaged to yield an index of the accuracy of measurement for the different conditions.
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