Not @NoLand but Norbert Kehrer:
HP Calculator Emulators for the Atari 800XL and for the Commodore 64
I wrote emulators for [HP-35, 45, 55 and 80] for the Atari 800XL and for the Commodore 64, which simulate the 4-bit HP calculator CPU to interpret the original program ROMs of the four models.
Screenshot images from the website:
via HPmuseum forum where Craig Bladlow notes
Norbert Kehrer was interviewed recently on the FloppyDays Vintage Computing Podcast, episode 96, by Randy Kindig