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The HP-18C is a Hewlett-Packard business calculator which was quickly followed by the very similar but greatly improved HP-19B. The HP-18C is HP's first RPL-based calculator internally,^[1] even though this was not visible on user-level in this non user-programmable model. The user has a solver (another HP first) available, but only had about 1.5 KB of continuous memory available to store equations.

The calculator has many functions buried in a menu structure. The clamshell design is fairly robust, but the battery door is the shortcoming of this whole line; 18C, 19B, and 28C/S models.

The HP-18C was introduced in June 1986.^[1]

References

^ ^a ^b Wickes, William C. (1988-10-01) [14–18 June 1988]. Forsely, Lawrence P. (ed.). RPL: A Mathematical Control Language. Proceedings of the 1988 Rochester Forth Conference: Programming Environments. Vol. 8. Rochester, New York, USA: Institute for Applied Forth Research, Inc., University of Rochester. pp. 27–32. ISBN 978-0-91459308-9. OCLC 839704944. Several existing operating systems and languages were considered, but none could meet all of the design objectives. A new system was therefore developed, which merges the threaded interpretation of Forth with the functional approach of Lisp. The resulting operating system, known unofficially as RPL (for Reverse-Polish Lisp), made its first public appearance in June of 1986 in the HP-18C Business Consultant calculator. (NB. This title is often cited as "RPL: A Mathematics Control Language". An excerpt is available at: RPLMan from Goodies Disk 4 zip file)