HP10s Calculator

In 1977, Hewlett-Packard introduces the smallest HP calculator to have a built-in printer and easily held in one hand. The HP 10s did not use RPN and had only + - x - and % keys. The first ten series (HP 10s) looks like the original HP 35 - white keys for digits, blue keys for simple maths functions, and black keys for the more advanced functions.

HP10s Timeline:

HP 10 - HP Calculator Simple Calculator : 1977
HP 10C - HP Calculator Programmable Scientific : 1982. HP 10C comes with 79 lines of program memory and 10 storage registers.
HP 10B - HP Calculator Business Calculator : 1989
HP 10bII - HP Calculator Business Calculator : 2001