approximate positions of fiducial marks, offsets for 
principal point) 
d. The real time program is headed by a control routine 
which checks whether an orientation step has been chosen. 
If not it branches to the main program. 
6. The main program has been written in a rather similar 
fashion to the Bendix AP/C program with the following 
changes (see Fig, 2) 
Fig. 2 
The AP/c-3-IBM 1130 program structure 
a. 1. The exchange data command transfers every 32 msec a 
total of 34 words between the 1130 core memory and the 
viewer interface buffer. 
2. This permits to transfer characteristic bits whenever 
a particular input is in operation. 
3. Therefore it is possible to test for this input at 
the beginning of the program. 
4. The operations of various data inputs and outputs , 
previously carried out every 1/5 sec (every 6^ loop) 
can now be handled every 1/30 sec (every loop). 
5. Due to the nature of the cycling the Exchange Data 
command must be combined with a wait-routine . 
The most important of the routines listed in fig. 2 are 
real time entry and the real time computation . 
They contain 
a. Scaling of 2 jji m inputs and adding to coordinate values 
b. coordinate transformations, 
c. checks for maximal velocity and acceleration,