I also have a hobby interest in HP calcs (own a 15-c), so double interest here. Not sure if you're a blogger, but that is some legitimate history with the early usage of handheld computing to aid science & engineering. A blog post would be great, but I'd settle on a reply here.
Here's what my dad wrote when I asked him:
The work often involved transmission line impedance calculations. These and other power calculations required a great many translations of rectangular to polar coordinates and back again. We had an Oliveti vacuum tube machine in the office that would only do this one operation in one direction or the other. Otherwise it was back to slide rule, pencil and paper. We had an IBM 360 in the basement that would do grid system power modeling. These calculations required 24 hours to get an answer.
Mom got me an HP-35 for Christmas. It was like touching an alien spacecraft technology.
Later on around 1976, I operated a consulting and substation design business. In this activity I needed to do hand calculations of short circuit current for industrial customers again using the HP-35. The HP-35 was an important tool and a real game changer for electrical engineering work.
I found this to be very good: http://www.hpmuseum.org/software/soft41.htm
And I've got this book from 1976: https://www.abebooks.com/book-search/isbn/0830668535/
It covers several different calculators too.
