digital pen plotters this is acomplished by use of a turret pen with pen widths varying from .3mm to l.émm. On a COM device there are usually methods for varying spat size and spot intensity under program control. For extremely large characters it is possible to replace each vector by a number of parallel vectors to increase the line width beyond that obtainable by varying pen or spot size. Ref. 3-10 contain numerous examples of these techniques as applied to actual publications.
On the device we used, the output using the Hershey characters was limited by tape speed, roughly 60 characters per second. As an example this text, which contains 24,000 characters required 400 seconds to process on the FR-80. COM devices containing internally stored fonts operate at a much higher speed — roughly 5,000 characters per second. As an example, the half million or so characters in Appendix E were produced in about i00 seconds using the internally stored characters which are supplied with the FR-80.
Higher speeds could also be obtained for the Hershey characters by writing a special program for a particular COM unit in which some of the characters resided in core in the mini-computer, or on an attached disc. Such an approach has in fact been implemented by one manufacturer.
6. Acknowledgments
The authors wish to acknowledge the assistance of Steve Soroka in preparing the program to produce the pictures in Appendix B, to Mrs. Carla Messina for the program to interface the NBS typographic system with the Hershey system, to M. Leighton Greenough for editorial advice, to Mrs. Constance Seymour for assistance in preparation of the manuscript and last, but not least, to Dr. A. V. Hershey. He deserves our thanks,and that of the readers as well, not only for having developed such a remarkably useful and important system but also for the generosity with which he has shared the fruits of his labor with others.
