of the fact that the monocomparator requires two persons. 
Of the four or five smaller organizations that apply 
(or plan to soon) analytic photogramme try productively, all 
of them utilize the rnonocomparator system. The stereocom 
parators have generally been applied only to large national 
programs. 
Relative to accuracy, a good rnonocomparator having a 
least count of one micron can be so adjusted and calibrated 
that its standard, error is less than 1.5 microns. 
The PUG 
One must not overlook the importance of the PUG (the Wild 
stereoscopic image transfer device) to the development and 
encouragement of analytic aerotriangulation, thanks to the 
vision of the manufacturers and to photogrammetrists in Austria 
and the Netherlands. Without some such device, the monocular 
system cannot function. In addition, the device has permitted 
accuracies beyond all moderate expectations. Even if a 
s tereocomparator is applied, the PUG idea is still required 
in two ways: (1) to transfer images to adjacent strips of 
photographs; and (2) to mark all images on one photograph in 
order to identify an image for later utilization in compilation 
plotting. It may seem strange that the PUG is also being 
used even in satellite geodesy to provide discreet, identifyable, 
precise reference marks. 
Relative to accuracy, the root-mean-square value of the 
parallaxes for an entire strip of good photography has several 
times been less than three microns, including all causes, 
attesting to the high quality of the PUG operation. 
Semi Automatic Comparators 
The photogrammetrist soon becomes impatient with the slow 
speed of measurement of image coordinates for analytic 
computations. This is generated partly by the importance of 
the redundancy of observations needed to establish the required 
statistical reliability of measurements. In an effort to 
improve the speed of operation, the stereocomparator at 
Aberdeen, Maryland has been equipped with a "joy stick" 
control so that the operator can traverse (slue) diagonally 
from one location to the next. 
To aid in solving the speed difficulty, the General 
Aniline and Film Corp. of Binghamton, N.Y. exhibited a 
"semi-automatic micro densitometer" at the American Society’s 
Annual Convention in March, 1964. Although the device was 
not arranged for analytic aero triangulation, it presumably 
could be used to record the coordinates of images with high 
speed and accuracy. It included a viewing screen that 
enabled the operator to see approximately where the measuring