HP-35
To calculate in style. The Hewlett-Packard HP-35 was the first pocket size scientific calculator in the world. This indirect killed the sliderule. It uses RPN, reverse polish notation. It is made from 1972 to 1975. Introduction price was around 400 Dollar.
It first was named the calculator but later Bill Hewlett gave it the name HP-35 because it had 35 keys. The first units had some bugs like 2.02 ln ex resulted in 2 rather than 2.02 (I checked, mine gives 2,02)
Mine is made in week 43 1971 and has serial number 7956 so a very early version. As far as I know the first week of production.
I made a new battery pack and hans give me an original manual:
original Dutch manual