Here is the museum of HP calculators.
When I was 13, my dad brought an HP-65 home from the office for the evening. I was hooked; I spent about three hours ditching homework, just punching buttons and figuring the thing out. (He still has it. It still works).
HP programmable calculators just rock. When I was 15, I got (in an, er . . . rather complex set of negotiations) an HP-25C programmable calculator. It was my first personal programmable device. With 49 steps of program memory that didn’t go away when the calculator was turned off, it was the bee’s knees until I got my first computer. I programmed the heck out of that thing. I skipped classes to program. I couldn’t *quite* get a MasterMind scorer in 49 steps (two of them had to be manual). This early exposure to tight-resource computing proved useful later on .
[Every HP owner in high school has had this moment: The classmate next to you asks to borrow your calculator. You say, “Sure!” and hand it over. They start pecking away, then pause. Longer pause. “Hey, where’s the ‘Equals’ key?” You just grin…]
When I joined Atari and started writing video games, I had a little extra money, and bought an HP-16C. I couldn’t really afford it, but it helped out a lot when I was doing low-level debugging. The 16C is, in my opinion, the best calculator that HP has ever made (and I own a number of others, including the 41C and several versions of the 48).
I read some books on synthetic programming on the 41C. Basically, some bugs in the firmware let you drop down into the native instruction set. It was interesting, and kind of cool to see the inner workings of things, but not that interesting if you’ve got real computers around to program.
Computers just don’t cut it for calculators. It’s a UI thing; a calculator is always immediately available: Just turn it on and you’re working. On a computer you have to find the calculator app, make sure it’s in the right base, then type in expressions whose keys are located all over the QWERTY keyboard. And if you’re doing systems programming, the computer that your calculator is on has probably just crashed….
A world without HP calculators would be a poorer place. I’m glad they’re making some kind of comeback. Of course, all of the folks who did the designs are probably gone, they’re just porting most of the existing stuff to newer, less proprietery hardware. Still it’s good that they don’t die altogether.
 My current target platform is a 13Mhz 68020 with a megabyte of ROM and a megabyte of RAM. It’s amazing what you can cram into such a tiny box with a good team of people.