An HP-18C in the state used for operating it. When not in use or for transport, it can be folded together due to its [[clamshell design, so that its width becomes half of what it is in the image.|thumb]]

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,

Further reading

  • HP-18C on MyCalcDB (database about 1970s and 1980s pocket calculators)
  • HP-18C at HP's Virtual Museum