wire, and (3) aligning the subject parallel with 

 the orientation line and taking the picture . 



Reading Film 



A microscope with a calibrated stage 

 was used in the normal fashion to determine the 

 film measurements. Two glass plates served to 

 hold the film flat . 



The measurements were repeated five 

 times and any measurements obviously in dis- 

 agreement with the average were not used. 



Calculating Longitudinal Distances 



The calculation of longitudinal distances 

 consists of three steps: ( 1) F rom the left and 

 right pictures, determine OQ', the distance from 

 the O line to the perpendicular projection of the 

 first point, say P' . ( 2) Fr om the left and right 

 pictures, determine OQ" , the distance from the 

 O line to the perpendicular projection of the 

 second point of measurement, say P" . (3) Sub- 

 tract the lesser distance from the greater dis- 

 tance to determine Q'Q" . 



Calculation of OQ' 



OQ' is calculated from equation 10 (see 

 "Theory"). The use of this equation r equi r es 

 the deter mination of the distances AB, OD, OF, 

 and OG and the insertion of these values in 

 equation 10. 



Etetermination of AB. --The distance AB 

 is a constant. It is the distance between the 

 optical centers of the two cameras (as in fig. 3) . 

 The distance between the points on the outside of 

 the lenses, which roughly correspond to the op- 

 tical centers of the lenses, was measured with a 

 stee l tape. This distance was used for the value 

 AB. 



Determination of OP. --The distance OD 

 is a constant. It is the distance from the O or 

 reference line to the perpendicular projection of 

 the optical center of camera A, point D, (as in 

 fig. 3) upon the base plane. The base plane or 

 grid of the photographic measuring device was 

 leveled. A point, judged to be opposite the op- 

 tical center of the lens, was chosen on the out- 

 side of the lens barrel, and a plumb bob was 



suspended from this point. The distance OD was 

 then measured with a steel tape. 



Determination of OF . - -The determina- 

 tion of OF consists of four steps. (1) From the 

 left film, determine the proportionality factor 

 for the distance between the two grid lines that 

 lie on either side of the first point of measure- 

 ment (F). (2) Measure the distance from the 

 first point to the nearest line lying to the left of 

 this point (assuming that O line lies to the left 

 also). (3) Multiply this distance times the pro- 

 portionality factor. (4) Add the distance from 

 the O to the left line to the results of (3) to ob- 

 tain the total distance from O to F /the position 

 of point P' (the first point) as it appears in the 

 right picture/. Since the distance from the O 

 line to any other line is equal to the number of 

 that line, then this distance can be read directly. 



Determination of OG . - -The procedure 

 for the determination of OG is the same as that 

 for the determination of OF except the left film 

 is used instead of the right film . 



Substitution of AB, OD, OF, and OG into 

 equation . - -To obtain OQ', now substitute the con- 

 stants AB and OD, and th e va riables OF and OG 



10, / OQ' = OG (AB + ob) - (OD) (OF )7 

 AB + (OG - OF) 



into equation 



Calculation of OQ" 



Since AB and OD are con sta nts, we need 

 only determine the distances OF and OG from the 

 right and left fi lm respectively (as explained under 

 "calculation of OQ' ") and then substitute these 

 values into equation 10. 



Calculation of Q'Q" 



We ha ve n ow determined the two di s- 

 tances OQ' and O Q" . I f OQ" is larger than OQ', 

 then 0Q"_^ OQ'^Q'Q", the longitudinal distance 

 between Q' and Q" . And, since Q' and Q" are the 

 perpendicula r proj ections of the points P' and P", 



the d istance Q'Q" is also the longitudinal distance 

 p.p.. 



PERFORMANCE 



The performance of the machine can be 

 considered from the following four categories: 



10 



