HP-18C

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, 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.