„3. 
physical objects and not the specification has to be changed. 
In relation to the analytical instruments this means that the 
basic design concept is a deterministic one. In other words, the 
physical components of the instrument are supposed to operate in a 
predictable and predetermined manner. But the behavior of analytical 
instruments does not depend only on their physical components. The 
overall behavior of the instrument depends to a great extent on the 
software and can be changed by a different set of programs. This 
indicates why a strictly photogrammetrically oriented definition is 
quite difficult [2]. A simple example may help to introduce a more 
general concept of analytical instruments and eliminate the need for a 
definition by comparison with analog instruments. Let us look only at 
one handwheel and one carriage of an analytical instrument. The input 
from the encoder of that handwheel is interpreted by a program as a 
certain value X. Let us assume that the instructions in a simple real- 
time program governing the movement of the carriage are once X = aX and 
y = aX and another time x = bX and y = m sin Y. Then during the rota- 
tion of the handwheel in the first case the measuring mark will move 
along a straight line whose points are equidistant from both x and y 
axes, and in the second case along a sinusoid with amplitude defined by 
m and frequency by b and n (in this case X is interpreted as an angle 
with n determining the number of pulses per degree). Now it is obvious 
that a software invariant characteristic of these devices is the cap- 
ability to address a two-dimensional array. So a general definition of 
an analytical instrument may be: an analytical instrument is a finite 
state digital machine for real-time addressing of two-dimensional 
arrays. The number of states depends on the dimension of the carriages 
and the resolution of the encoders in the secondary or minor feed-back 
loops (e.g. for a 1 um resolution and carriage dimension 25 cm x 25 cm, 
the number of possible states is 6.25 x 1010 per carriage). 
Theoretically a photogrammetric analytical instrument is a 
special case of a general machine with p inputs and q outputs, capable 
of addressing r s-dimensional arrays in which the q outputs may be 
expressed by any function of the p inputs. The minimum configuration 
of the optical-mechanical component (for measuring and viewing) of a 
photogrammetric analytical instrument has three inputs (independent 
variables) and four outputs (dependent variables) capable of addressing 
two two-dimensional arrays. This component may be regarded simply as 
an input-output peripheral of the digital computer, designed exclusively 
for the purpose of addressing a special read-only analog memory - the 
photograph. It is worth noting that at present this optical-mechanical 
component bears a close resemblance to stereocomparators only because of 
the lack of technological means for building less cumbersome devices 
(e.g. electro-optical devices) with fewer moving parts, for more imme- 
diate addressing of photographs. This definition of a photogrammetric 
analytical instrument indicates clearly not only the high independence 
of the design from the functional relationships between the input and 
output variables, but also the high degree of modularity of such a 
system in regard to the choice of a specific computer and any other 
peripheral for communication with the computer, for external storage of 
programs and data, and for presentation of results. Except for the 
optical-mechanical component and its interface with the computer, all 
Other components and interfaces including computers, discs, tapes,