Virtual Si Museum /2122/ HP Calculators

My own collection of the HP Calculators. The HP 21 was my very first Hewlett-Packard calculator. Here sorted by its number with HP 15C as most recent addition: 

HP 9g Scientific Graphing calculator

HP 15C Scientific with Matrix & Complex Math

HP 21 Second Generation HP-35

HP 30s Scientific calculator with algebraic logic

HP 35s 35th anniversary of the HP-35

HP 48GX Graphing calculators using RPN and the RPL programming language

Virtual Si Museum /2111/ E.Eng Tools

This is how I was introduced to the engineering. My very fist log rule and my HP-21 scientific calculator (successor of the famous HP-35)

REF:

[1] Slide rule: https://en.wikipedia.org/wiki/Slide_rule

[2] HP-21 scientific calculator: https://en.wikipedia.org/wiki/HP-21