"Specialmatic was designed intentionally for job shop versatility and accessibility as well as for complete shop floor and operator control.
In essence, it took advantage of a tape-control-type mechanism but without the tape. With actual tape control, once the complete program tape had been prepared (typically away from the machine and off the floor), the sequence of machine operations and machine functions was fixed and shop floor operator intervention was restricted at most to manual overrides of programmed speeds and feed rates. With the Specialmatic approach, the program tape was broken down into segments, each corresponding to discrete program components (particular machine functions and machining operations). Instead of a tape, the operator was provided with a standard set of prepunched stainless steel "keys" that were inserted into a rotary drum optical reading system (like a tape reader) in the sequence required to produce a given part.
Thus, the program could be assembled by the operator himself, even while making a first trial part, and could be changed at will thereafter to optimize the program by altering the sequence or adding or subtracting operations. In addition, through the use of dials which permitted both coarse and fine tuning, the operator could set and adjust feeds and speeds, relying upon accumulated experience with the sights, sounds, and smells of metal cutting. There was no permanent storage of a particular program with Specialmatic, as was embedded in a tape, but it was easy enough to make a record of the sequence of keys and the dial settings for future automatic runs of the same part. The Specialmatic allowed the machinist to take full advantage of automatic programmable control and shaped the new technology in such a way that it served his purposes rather than undermined them. In Caruthers's view, that meant also better work, cheaper and simpler machines, more reliable production, and more jobs."
-- David Noble, Forces of Production