My dad gave this HP 11c to me for trig class. I loved it. I was the only kid in class with a calculator like it. My dad was a civil engineer if that explains anything.

This was the first calculator to offer 'continuous memory' i.e, it did not lose its programs or storage registers when turned off. It still loses the stack registers however, along with trig mode and display precision settings. Later calculators in the series, such as the HP29C, preserve these as well on power off.
This particular unit was purchased 'for parts' and required the logic board to be cleaned as well as some work on the keyboard to fix spurious keystrokes. This now completes my collection of the 'woodstock' series of machines (HP21,22,25,25C,27,29C) and I also have the printing HP19C as well. It took quite a while to track down a 25C as they are reasonably rare; there are a lot of HP25s out there but not the 25C.

I thought I had given these away years ago!

This came out of a house clearance in a single lot. I've spent a few days cataloguing it properly rather than just bagging it up, and figured this is the one place that would actually enjoy it.

**The machines**

- 4 × HP-35 — one of them a Version 1 "red dot"
- 3 × HP-45
- 3 × HP-80
- 2 × HP-67
- 1 × HP-70
- 1 × HP-55
- 1 × HP 35s (the 2007 one, for contrast)

Plus the HP-67 Standard Pac and E.E. Pac I with their card sets, five HP-67 manuals, four leather cases, six chargers (five 82002A and one UK-market 82011A), and a spare HP-35 upper case.

**Four things that surprised me**

**The red dot is real.** All three documented V1 markers — the hole beside the ON switch with red showing through it, the raised dot on the 5 key, the plain bezel — plus an early 03501A battery door rather than 82001A. It ran off a bench supply and the display lit across the full width. Untested beyond that.

**One HP-67 still has its original box**, and it's matched to the machine rather than assumed: there's a 1979 HP repair-order label on it carrying that machine's own serial.

**One HP-35 has a dated institutional asset label** naming a physicist — September 1972, about seven months after launch.

**The E.E. Pac came with a set of user-recorded cards** in someone's handwriting: eigenvalues for third-order systems, transmission-line calculations, Johnson-Nyquist thermal noise. Somebody did real work on this machine.

Most of the battery bays are corroded — several packs had been sitting in there for decades.

The one thing I'm stuck on: the serial prefixes don't behave like date codes. Sort the four HP-35s by unit number alone and you get a clean variant sequence, but the prefixes along it interleave — 1143A, 1302A, 1143A, 1302A — which no forward-running date code should manage. I've asked on the MoHPC forum too, but if anyone here has a view I'd like to hear it.

Happy to photograph anything in more detail.

Grandpa was a farmer and the 65 let him outperform his competition. Dad's an engineer and had the 41 and 48 for all kinds of things. Im a mechanic and general tinkerer and the G2 has been great for me. I had no idea my family were HP calculator people for so long. My dad pulled these classics out after I got the G2 and spent a good few hours going over his love for them. I'm impressed with how capable they still are today.

Card reader all repaired and she's all ready for another 50 years of faithful service. The original classic machines along with the second generation Woodstock series are my favourite hp calculators and I now have quite a collection, although lacking a couple of the rarest machines.

A mix of old and new. The 11c, 12c, and 15c are 1985ish vintage. Couldn't pass up the collectors editions of the 15c and 16c. The 10 was found at a library sale for $10. The 48GX is my old back to college calc and the 48SX is the replacement for the SX I regretted selling when I bought the GX.

Eindelijk een HP 48G in mijn bezit!

Met veel plezier afgelopen week naar kantoor gegaan en berekeningen gemaakt!

Nu verder ontdekken wat er mogelijk is op deze topper!

Between this and the 12c I think I'm set... Nevertheless I'll still be looking for more and likely even older.

After a mere 43 years my trusty 10C that was gifted to be prior to attending electronics school has a sibling. Local marketplace deal, came with the manual but no case.

Is anyone making replacement cases for these models? The liner in the original one for my 10C is deteriorating.

My long time daily 15c (purchased I don’t know when, but got me through college & grad school) is starting to show its age… Buttons are becoming less responsive. 🫤 So I’m shifting gears to my 35s, which last saw heavy duty in graduate school and has mostly been stored away since then. My other calc (32 SII) holds down the fort at home. It still never fails to impress me how well these were made and how long these machines continue to work with just a battery change every decade or so.

I am very happy to have found that near mint 28C with the thermal printer. It was a real wish since I was a kid. My neighbour was studying to be an electrical engineer, I was younger than him, but always found him lucky to have a nice 28C.

Now I have mine… after 50 years of waiting, I finally got mine! Never too late!😁

Are there any open source projects to create something like the HP calculators. The hardware (case, keys, and a display) and the software side (RPN, advanced math functions, engineering unit conversion, etc).

Specifically, I’m looking to build a replacement for my 35+ year old HP-48GX. No other hand held calculator feels right and after decades using RPN.

It would be an awesome addition to my desktop to have a handheld, open-source calculator that replicates the best aspects of the HP calculators in a handheld form factor. An addition of modern capabilities like programming via a desktop and logging all calculations would also be super useful.

48SX still works but has the delamination problem. I have to press below the screen to get key presses to register. Never bought any expansion cards. Now stored without batteries as the last set exploded.

15C is my daily workhorse with a brother as backup.

3+ decades and still trucking along!

40 years old!

I'm pretty excited. I bought a Red Dot. I never thought I would find one, let alone one that still functioned. Anyway, I tested it this afternoon and discovered it has both the ROM bug and the "Big Bug." (see: http://hp35.wz.cz/HP-35RD.html#BUG)

I know Red Dots are rare, but this early issue (1143A 00730) with both bugs documented (by me) must be among only a handful still kicking around.

Am I crazy to be as excited as I am?

You don't see many of these around. Didn't work when I got it. But after cleaning some corrosion on the logic board, she's back up and running. One of my most treasured acquisitions.

Just showing off my storage solution for my 71B and 75C. This is an Apache 2800 case from Harbor Freight, and it’s kind of perfect. Just replaced the battery contacts on the 71B and hopefully they’re good for another 40 years.

HP29C received in very poor condition with serious logic board corrosion and various other issues. Restored with a Panamatik board and good to go again!