Did yours have 4 slots on the end that you could plug in expansion modules? Inverse Polish notation? On mine, I used 2 of those expansion slots to add expanded memory, the third for a combined math/statistics module and the 4th port to add a card reader that inserted into the expansion slot then snapped onto the back of the calculator.
I got this calculator 1980 IIRC. I was a little over a year out of college and had outgrown the TI-59 that got me through the last few years of the STEM degrees.
My new HP calculator though, the company paid for. $1000 investment they made for me. Big $$$ HP enhancements plus one aftermarket math coprocessor that completely invalidated the warranty.
First the HP enhancements. HP had enhancement packs of programs that were available both for plugging into one of the 4 slots on the end or magnetic strip cards that were loaded via the card reader. I think the manuals you described in the 3-ring binder were documentation manuals for one or more expansion packs.
I had 3 or 4 expansion packs. I had a 3-ring binder with a plastic sleeve to hold strip cards containing lots of wicked programs and the manuals. For me, I was equipped with high end statistics, regression analysis and specialized engineering calculations.
Now, the aftermarket “bootleg” chip I bought sped up math functions about 3x. It came with several pages of install instruction and diagrams. Supposedly, it was a simple install, a caveman can do it. I read the documentation and got to part about soldering to the circuit board and power supply and hell no I'm not doing that!
We had at the facility an instrumentation and computer repair group. Computer wise, they worked on DEC minicomputers and IBM mainframes. Called them up and said I needed a computer worked on. They said fine and a tech would be right over to take it to the shop thinking it was file cabinet size. I said no thank you, I'll drop it off, which the computer guy was surprised at.
I get to the repair shop and hand over the calculater and box with the chip + instructions. I need this chip installed in this calculator. He said, we don't work on calculators. I said, this is a computer and I need a chip put in it. When I called the calculator a computer, it was a magic word and he said sure. My calculator and stuff went from me to him, they did their magic and it was ready in a few days. Perfect.
Function changes to the HP calculator were made. The charging port was snapped out and the its wiring capped off. In its place, a switch was added that turned the coprocessor on/off. The OEM rechargeable battery pack was snapped out and replaced with a OEM blank that held standard AA batteries. The calculator ate up batteries. I always had fresh batteries wherever I went. Used this calculator from about 1980 until I retired a few years ago.
It was probably an HP-41CV with a card reader. I had one of those for a while, too, c. 1981.
Then I got an early IBM-PC in Spring of ‘82, and most of my serious number crunching happened there. One of the great things was taking a graduate level numerical methods class, and most everyone else was having to trot down to the computer center and use time share terminals on the CDC Cyber mainframe.
Me, I was using interpreted BASIC off of the motherboard ROM on the IBM-PC in my apartment. I’d write these programs to do numerical solutions for big nasty diff eqs, and some would take 5-6 hours to converge to a solution. But that was OK, I’d get things set up, do a test run to make sure it looked like all was well, that it was converging, fire it up for the final run, then go to bed! In the morning, I’d print the results on my Epson MX-80 dot matrix printer. Beat the heck out of having to go to the computer center!
Yep - it had the card reader and some other stuff. I’m a pack rat so that binder of instructions was difficult to throw out. (It had survived 20 years of previous clearing-outs of the clutter).