Valentín Albillo is a Spanish pioneer in HP calculators. He has been writing articles about several HP calculators and computers for a long time. He has a soft spot for the HP71b, but he has written articles for most of the HP vintage models.
I had a page linking to his articles in his previous website, but now that that one is down, hpcalc.org has hosted Valentín's articles in their website. I just had to update the links to the new site!
You can find here the page that links to all of Valentín's articles:
And here you have one of them, describing, praising and using my preferred calculator: the HP15c: