HEWLETT PACKARD H28C vintage calculator.

HP-28C was graphing calculators produced by Hewlett-Packard from 1986 to 1992. The HP-28C was the first handheld calculator capable of solving equations symbolically. This models were produced, the HP-28C came first in 1987 with 2 kilobytes of usable RAM, and was the first handheld calculator with a Computer Algebra System.