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the PLOTTER routine. "The main software then processes the information so 
encoded in the switch status words in the same way as if the real switches 
were operated on in the analytical plotter. 
Coordinate Input Control. Manual input X, Y, Z to analytical plotters can be 
accomplished with various control elements, such as handwheels, footdisk, 
joystick, trackball, handdisk, cursor etc. Regardless of its type, each of 
these input elements generates a train of pulses which are incrementing 
appropriate model registers or photo D-registers. In the simulation approach 
the best way is to display a graphical rectangular array representing the 
range of a joystick operation for the X, Y input. With the origin in the 
centre all other discrete interaction-sensitive positions in the array are 
assigned the meaning of suitably increasing positive/negative increments in X 
and Y direction. Similarly, a one-dimensional array of positions displays a 
suitable range of Z-increments. During the simulation run the operator 
activates a suitable position in the arrays, as if he would operate a 
joystick. The input control part of the PLOTTER routine will use the 
specified values to increment the pseudoregisters, as described above. The 
incrementation of pseudoregisters will continue in each calling cycle to 
PLOTTER until the input is deactivated by selecting a zero-increment value 
positioned in the centre of the pseudo-joystick arrays. The currently active 
position within the arrays is always graphically marked to allow the operator 
to monitor the input process. 
Hardware Output 
Digital Displays and Counters.  Console-mounted digital coordinate and 
parameter displays must be simulated on the interactive screen. For 
analytical plotters with a time scheduled continuous display outputs on the 
video terminal the simulation is not needed. In the opposite instance, the 
interactive terminal will display appropriate numerical values in suitably 
positioned annotated counters. The COUNTERS part of the PLOTTER routine takes 
care of the scaled transfer of the contents of individual pseudoregisters. 
Optics. The main feedback for the operator control of a regular analytical 
plotter operation comes from the optical system. Even though a simulation of 
a measurement process controlled through the optical system is not meaningful, 
it is still important to simulate at least a limited joystick-controlled 
displacement of measuring marks in fictitious optical fields. They are 
displayed on the interactive screen as windows with a centrally located fixed 
measuring mark. Small changes of the pseudoinput X, Y, Z are reflected in the 
optical windows as corresponding displacements of optical pseudodetail 
represented on the screen by a suitable symbol. The displacement is 
controlled by the OPTICS part of the PLOTTER routine. By using this option 
one can simulate the introduction or elimination of small errors in recorded 
pseudomeasurements and effect a more realistic computation of not-only-zero 
elements of transformations and orientations involved in the fictitious run of 
the analytical procedure. 
Control of Simulation 
In on-line operations any individual operator-plotter interaction, with the 
exception of unscheduled breaks and interrupts, can be effected only at times 
during which the program anticipates operator's input by interrogating the 
State of switches and contents of registers. The program control is running 
in indefinite cycles temporarily suspended or eventually terminated when 
operator's commands are detected. These cycles are usually programmed to 
collect and process measurements either in the stereocomparator mode or in the