Comment by ndiddy

HP's Voyager calculators originally ran on custom silicon-on-sapphire chips (which gave them extremely long battery life). After these stopped production, HP changed the calculator design to use an off-the-shelf microcontroller that runs the original firmware in an emulator. This reduces the battery life, but the emulator runs the firmware 60-90 times faster than the original calculators. This is baseless speculation, but I imagine what happened was that they either tried switching microcontrollers or otherwise updated the emulator and introduced an emulation bug that gets exposed by the calculation in the blog post.