The HP 18c was the first in a series of “clamshell” calculators produced by HP. The HP 18c opens like a book with two keyboards facing each other inside. The HP 18c included graphing and a date-time-alarm feature similar to a personal organizer. The 18C had 2K of memory and it used algebraic logic with parentheses (but no precedence) and the multi-line display.
1986 - 1988