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The influence of tobacco smoking upon operator’s precision with 
photogrammetric instruments 
Introduction 
Tobacco smoke contains nicotine, tar, carbon and other substances 
which are inhaled by the smoker. This is an investigation of the possible 
influence of smoking upon stereoscopic vision. 
Experimental Design 
Stereoscopic models were formed from aerial photographs placed in 
the Wild and the early type of Zeiss stereocomparator. Clearly identi 
fiable points in the models were selected for measurement. The paral 
lax in each point was measured stereoscopically with 25 measurements 
forming a series. Several series were measured before and after heavy 
smoking. A mean value (px, py) and a standard deviation (s px , s py ) 
were computed from every series. The data were then compared to 
decide the influence of smoking. Three operators took part in the tests 
during a period of two days. Assistants read and recorded their mea 
surements. Operator No 1 measured the horizontal parallaxes of two 
different points in the Zeiss comparator. Operators Nos 2 and 3 mea 
sured the horizontal and vertical parallaxes of the same point stereo 
scopically in the Wild comparator. 
Statistical Treatment of Data 
Differences between the standard deviations in the series measured 
by the same operator were analyzed by Bartlett’s test. In most cases 
this test shows a wide variation in the precision. Therefore we cannot 
use variance analysis to investigate the differences of the mean values 
as it is impossible to state whether the differences depend upon the 
standard deviations or the mean values or both. However, a difference 
between two mean values can in any case be tested with a t-test even 
if the standard deviations differ. The difference between two standard 
deviations is tested with an F-test. (See reference No 1 for more details 
on statistical procedure.) 
Residts of Tests 
The two points measured in the Zeiss comparator were not equally 
clear in identification. This was evident from the standard deviations. 
One day the precision was uniform, the next day it varied. In both 
cases an analysis showed differences between mean values which were 
higly significant. The influence of smoking could not be isolated. 
In the Wild comparator px and py were measured in the same series. 
The differences between s px and s py in the same series were not signi 
ficant for any one operator. A study of the variation of s px and s py 
during the course of a clay indicated a uniform s py for operator No 2