Compared to the AP/C-3 of the year 1972 all analytical plotters 
now have a 24 K 16 bit core memory instead of an 8 K memory; 
this now leaves adequate room for additional programming and for 
control by a variety of devices such as the CRT and a teletype. 
While the CRT has certainly improved the effectiveness of a 
man-machine dialogue, the panel oriented Standard-user friendly 
operation has persisted with some instruments, or it can be used 
in addition to the CRT. 
The digitization increment of 2, 1, 0.625 or 0.5 pm is more of 
a token than a real standard, since most likely none of the 
instruments is designed for a higher overall accuracy than t 5 ym. 
All analytical plotters use closed loop servo systems to ascertain 
this accuracy. 
Some instruments use linear encoders (e.g. US-1, AP/C-4, Traster) 
and may be more stable than those with pure spindle encoders (e.g. 
AP/C-3T, C 100); when the temperature remains constant, however 
and when a "self-calibration" is made occasionally the 3 pm can 
nevertheless be maintained. 
Concerning the computers in use the cycle time indicates, that 
compared to 1972 the speed of computation has become 3 to 6 times 
as fast. Interesting is also the added computer hardware such as 
1. floating point hardware 
2. multilevel interrupts 
which greatly facilitate the programming ease in computer 
language and program structure. 
Digital stereocartograph and the stereocord are open loop systems. 
But since step motors seem to work reliably nowadays or since 
these instruments may perhaps be thought of as working with a 
more limited (second & third order) accuracy, this may be 
acceptable. 
The usefulness of a larger core may be demonstrated by looking 
at the type of software needed for an analytical plotter: 
It is composed of an operating system to be stored in core (moni- 
tor, disk operating, assembler or compiler). It further includes 
applications software in core (real time program) or on disk 
(orientation programs, service programs). 
A 1972 system only permitted a considerably lers sophisticated 
operating system with a small common area. In a 1976 system the 
operating system may be 8 times larger and the common area is 
2.5 times as big for greater convenience.