Valentin Albillo's HP Collection

Back Home

HP Calculators

HP Calculator Pictures

Here you'll find a set of pictures I've taken myself featuring HP calculators from my own personal collection, together with useful details and my (hopefully interesting) anecdotes and comments on each particular model, including links to relevant materials (Articles, Brochures, Challenges) previously uploaded by me to this very site. Enjoy!


jpg HP Picture VA100 - HP-10C

This is my HP-10C, the simplest HP Voyager series' model and the last to be released back in 1982. After 37 years (as of 2019), it still looks and works great.

Unbelievable quality for such modest unit and its very simplicity (just the one yellow prefix key) in the iconic landscape Voyager form factor make it a very appealing calc to behold, I know that I like it very much. And as it didn't sell well it's become a very rare vintage calc indeed, you'd be hard-pressed to find one in mint shape like the one shown above.

Anyway, despite its simplicity it still boasts the same awesome physical quality, including "eternal" battery duration, but it has a much reduced function set and capabilities as compared to the HP-11C (let alone the HP-15C), though still programmable and featuring all the usual scientific and statistic functions (including linear regression), engineering display mode and flexible storage allocation (from 10 storage registers and 9 lines of program memory to no registers and 79 lines).

jpg HP Picture VA101 - HP-10C

This is my HP-10C, the simplest HP Voyager series' model and the last to be released back in 1982. After 37 years (as of 2019), it still looks and works great.

See the full description and other details in the link above this one.

jpg HP Picture VA102 - HP-10C

This is my HP-10C, the simplest HP Voyager series' model and the last to be released back in 1982. After 37 years (as of 2019), it still looks and works great.

See the full description and other details in the link above this one.

jpg HP Picture VA103 - HP-10C

This is a close-up detail of my HP-10C, the simplest HP Voyager series' model and the last to be released back in 1982. After 37 years (as of 2019), it still looks and works great.

See the full description and other details in the link above this one.

jpg HP Picture VA110 - HP-11C

This is my HP-11C, the first Voyager I owned, which was given to me back in 1981 as a present by a close friend. Some present !. It was love at first sight so I took it with me to a very harsh, desertic environment for a long time and it never let me down, it worked perfectly and still works and looks as new nearly 40 years later, with just two battery changes in those 4 decades. How's that for quality and durability ?

The HP-11C has always been shadowed by its more capable sibling, the HP-15C, but that doesn't mean it hasn't got what it takes, on the contrary. In addition to the usual full range of scientific and statistic functions, it also features a handy random-number generator (at long last!), hyperbolics, factorial, combinations and permutations. Its programming capabilities include label addressing, insertion, deletion, 4 levels of subroutines, increment/decrement loops, indirection, flags, user mode and last but not least, 63 program steps and 21 registers, 20 of which can be converted to additional program steps for a maximum program length of 203 fully-merged steps. You can do a lot with all that.

Have a look at this Article of mine (fittingly, the very first I wrote) for a detailed review including a nice sample program for you to see for yourself what it can do with ease:

Long Live the HP-11C, (includes a program to quickly and accurately find the sum of infinite alternating series, even divergent ones)

jpg HP Picture VA111 - HP-11C

This is my HP-11C, the first Voyager I owned, which was given to me back in 1981 as a present by a close friend.

See the full description and other details in the link above this one.

jpg HP Picture VA115 - HP-11C

This is the back plate of my HP-11C, the first Voyager I owned, which was given to me back in 1981 as a present by a close friend.
Note: the Serial Number's last 5 digits have been replaced by 0s for privacy reasons.

See the full description and other details in the links above this one.

jpg HP Picture VA121 - HP-12C

This is my mint HP-12C, the last Voyager I got. At first, I didn't like financial models at all, I was interested only in scientific calculators so I gave the HP-12C a miss. However, once I had all Voyagers except the HP-12C I got one and, much to my surprise, discovered that it was a very capable machine and despite its many limitations you could do about everything with it if you took the effort to try, sort of a worthy challenge. Just for instance, I was able to fit all 6 trigonometric functions accurately within a single program. I also discovered that it had the best polynomial root finder and polynomial evaluator in the whole series, easily surpassing the HP-15C in that regard. It was also possible to program the Gamma function, do integrals, solve differential equations, even play games, so I got to really like this very capable little machine which, come to it, could actually do everything.

The HP-12C has proved to be extremely resilient and sells well after all other HP calcs of its time were long retired, with new, more capable versions being released (though I only like the classic, original one). Have a look at these Articles of mine for a detailed review and several highly uncharacteristic (non-financial) sample programs for you to see what you can do with it if you dare to try:

Long Live the HP-12C, (includes a program to play a game of Bridge-It vs. the HP-12C)
Tried and Tricky Trigonometrics, (fits all 6 trigonometric functions accurately in a single program)
HP-12C Serendipitous Solver, (finds roots of, and evaluates, Nth-degree polynomials quickly and accurately)

jpg HP Picture VA151 - HP-15C

This is one of my HP-15C, the most capable Voyager Series model, a real marvel of engineering with the best ergonomy, most advanced capabilities and batteries that last forever. What has this model to offer over the HP-11C ? Well, it has Integrate and Solve, which can be nested with Integrate and vice versa. It has full complex number functionality, including arithmetic, transcendental functions and even a parallel complex RPN 5-level stack. It's got more than twice the memory. It has full matrix functionality including arithmetic, determinant, inverse, transpose, linear system solving and utility functions to help deal with complex matrices. Of course it's got all the HP-11C functions such as Gamma, hyperbolics, combinations, permutations, statistics, linear regression and random-number generation. And last but certainly not least, advanced programming capabilities such as labels, 10 flags, all 12 conditional tests, 7 levels of subroutines, indirect addressing, loops, recall arithmetic, User mode, the works ! Even synthetics !

In short, a dream machine, the best scientifc calculator of its kind. About the only negative points are that it doesn't support alphanumerics (so program steps are seen as numeric keycodes, which is rather tiring for listing and editing) and that it's pretty pretty slow. Batteries last forever but its CPU executes only ~4,400 microcode instructions per second and it shows. Besides the many Challenges and Mini-Challenges featuring the HP-15C which you can find in the HP Calculator Challenges section, have a look at these Articles of mine for a detailed review, including nice sample programs for you to see for yourself what it can do:

Long Live the HP-15C, (includes a program to compute Euler's constant e=2.71828+ to more than 200 digits using matrix operations)
HP-15C Nth-degree Polynomial Fitting, (fits an Nth-degree polynomial to a set of data)

jpg HP Picture VA152 - HP-15C

This is one of my HP-15C, the most capable Voyager Series model, a real marvel of engineering with the best ergonomy, most advanced capabilities and batteries that last forever.

See the full description and other details in the link above this one.

jpg HP Picture VA160 - HP-16C

This is my HP-16C, a fantastic HP calculator with the outstanding quality inherent to all Voyager Series models, and which still looks and works like new despite being nearly 40 years old by now (2019).

The HP-16 is a specialized calculator intended for programmers (though I've never used it professionally), which natively works in bases 2, 8, 10 and 16 with word sizes from 1 to 64 bits. It features all kinds of dedicated operations such as shift and rotate functions, masking, bitwise logic, double precision multiplication and division, plus standard floating point arithmetic with square root and 1/x, and advanced programming with labels, loops, subroutines, flags and tests. It also has reallocatable memory between program steps and registers where the number or registers depends as well on the specified word size.

Precisely that very feature, increasing the number of available registers by decreasing the word size, is made good use of in this article I wrote dedicated to the HP-16C:

Long Live the HP-16C, (includes a program to solve the Hanoi Towers puzzle with N disks)

jpg HP Picture VA161 - HP-16C

This is my HP-16C, a fantastic HP calculator with the outstanding quality inherent to all Voyager Series models, and which still looks and works like new despite being nearly 40 years old by now (2019).

See the full description and other details in the link above this one.

jpg HP Picture VA169 - Voyager Series leather case

This is a leather-like case for all models of the HP Voyager Series, i.e.: HP-10C, HP-11C, HP-12C, HP-15C and HP-16C. It perfectly fits and keeps them well protected besides looking real classy. I got one for every Voyager calc I own plus another one for my HP42S as well. Recommended.

jpg HP Picture VA250 - HP-25

This is my very first HP calculator, the wonderful HP-25, the smallest and cheapest HP programmable calculator at the time. Released in 1975 (some 44 years ago as of 2019) it still looks and works perfectly.

It has 10-digit with 2-digit exponent, classic RPN stack, 8 storage registers with full storage arithmetic, a vast range of math functions including statistics, solid build and very small size, bright LED display fully useable in very low light or even utter darkness, excellent reliable keyboard, extremely good and comprehensive documentation (including tons of good application programs for all disciplnes), good programmability (49 fully-merged steps) with tests, branching, and single-step execution for debugging, etc. Also, an updated version, the HP-25C, dotted it with Continuous Memory, another first at the time.

You'd need to have lived through those times in order to fully understand what the HP-25 meant for both professionals and students like me back then, but failing that, you can find some of my programs for it in the HP Calculator Programs section in this very site, which will give you a fair idea. Also, you should really have a look at this Article of mine for a detailed review including two truly amazing sample programs for you to see for yourself what it could do when pushed to the max:

Long Live the HP-25, (includes two programs to solve 1st-order ordinary differential equations using Runge-Kutta methods of 3rd and 4th order, resp.)

jpg HP Picture VA251 - HP-25

This is my very first HP calculator, the wonderful HP-25, the smallest and cheapest HP programmable calculator at the time. Released in 1975 (some 44 years ago as of 2019) it still looks and works perfectly.

See the full description and other details in the link above this one.

jpg HP Picture VA252 - HP-25

This is my very first HP calculator, the wonderful HP-25, the smallest and cheapest HP programmable calculator at the time. Released in 1975 (some 44 years ago as of 2019) it still looks and works perfectly.

See the full description and other details in the link above this one.

jpg HP Picture VA280 - HP28S

This is my HP28S, a Saturn-based model, the one and only RPL model I own which I bought just because I liked the form factor: foldable with a large graphic screen and twin keyboards, very elegant and ergonomic (save for the dreaded battery door). Right now it's 31 years old (as of 2019) and absolutely mint, matter of fact it's NIB actually, I've never ever used it other than to take these pics.

Back then it was a truly revolutionary model, a quantum leap in terms of paradigm and functionality over anything existing at the time, which essentially doomed classic RPN for good. It does symbolic math, has named variables, lots of data types, a very extensive function set, a powerful Solver, infrared printing, graph plotting, math in bases 2,8,10 and 16 with word sizes from 1 to 64 bits, catalog of all functions with their argument syntax, ... plus directories, custom menu, extra graphics manipulations. Last but most certainly not least, it has 32 Kb RAM instead of the nearly useless 2 Kb of its previous incarnation, the HP28C (which should've never been released with such crippling specification.)

jpg HP Picture VA281 - HP28S

This is my HP28S open flat, a Saturn-based model, the one and only RPL model I own. It's 32 years old as of 2020.

See the full description and other details in the link above this one.

jpg HP Picture VA283 - HP28S

This is my HP28S, a Saturn-based model, the one and only RPL model I own, 31 years old as of 2019.

See the full description and other details in the link above this one.

jpg HP Picture VA284 - HP28S

This is my HP28S, a Saturn-based model, the one and only RPL model I own, 31 years old as of 2019.

See the full description and other details in the link above.

jpg HP Picture VA289 - HP28S

This is the back of my HP28S, a Saturn-based model, the one and only RPL model I own. It's 32 years old as of 2020.
Note: the Serial Number's last 5 digits have been replaced by 0s for privacy.

See the full description and other details in the links above this one.

jpg HP Picture VA320 - HP-32S

Behold my NIB (literally!) HP-32S !. Released in 1988, it was an inexpensive ($53.86 here) but powerful calculator, truly small and lightweight, which many (yours truly included) prefer to its sequel (the HP-32SII) for his elegant, non-cluttered keyboard (made possible by its menu system) yet it has a comprehensive function set including hyperbolics, Solver, Integrate, bases 2,8,10 and 16, statistics and complex-number support for arithmetic and transcendental functions. Alas, no complex stack a la HP-15C and no built-in matrix operations either.

Instead of the usual RPN registers, it has 27 variables (A-Z + i for indirection) which are allocated and deallocated on the fly to make the most of its somewhat meager 390 bytes of RAM available to the user for data and programs, which could use up to 7 levels of subroutines, indirection, looping, conditional tests, flags, labeled I/O and last but not least the excellent Solver which could solve for any variable. Also, batteries last for very long (though not as long as the Voyager Series' models, mind you).

jpg HP Picture VA321 - HP-32S

One of my HP-32S, a most excellent and much loved classic RPN calculator, small, elegant, lightweight and powerful.

See the full description and other details in the link above this one.

jpg HP Picture VA325 - HP-32SII

My HP-32SII, a 1991-released improvement over the original HP32S in some aspects, not so much in others. In particular the keyboard has a second shift key and frankly it's way too cluttered, but it does add equations and fractions for extra power.

See the HP32S description for extra details in the links above this one.

jpg HP Picture VA351 - HP-35s

My HP-35s, an early model which was presented to me at the time it was released. It's in the style of vintage HP RPN calculators, trying to mimic their classic look-and-feel while implementing modern advanced features such as algebraic equations (which can be used as alphanumeric prompts), complex-number and 3D-vector operations, Solve, Integrate, fractions, non-decimal bases, and good programming features plus a 2-line x 14-character dot-matrix LCD display and much more memory, 30 Kb, which is good for 800+ registers (each of which can contain a 3-valued vector, so theoretically you can store ~2,400 floating-point values at once). Alas, it has no mass storage capabilities at all such as a card reader, let alone USB, so you can't save/load your programs and data. On the positive side, it uses two CR-2032 batteries which last for many months.

Most regrettably, it also has many bugs (20+ and counting), some of which are quite annoying or even show-stopping, which HP never bothered to correct. Furthermore, some important features are very poorly implemented, such as complex-number and vector handling, with many important operations and functions missing, even pretty basic ones. Same for non-decimal base operations and last but not least, it's slow as molasses. All in all, it makes for a poor user's experience, which is a real pity as otherwise the machine would be quite powerful and enjoyable to use.

Have a look at the following articles I wrote which extensively discuss and feature the HP-35s:

Storing Lotsa Lotsa Numbers, (short routines to conveniently store and recall more than 2,300 floating-point values in the indirect variables)
Boldly Going - Going Back to the Roots, (program to very quickly find real/complex roots of arbitrary equations with real/complex coefficients, as well as programs. Faster than Solve)

jpg HP Picture VA352 - HP-35s

My HP-35s, an early model which was presented to me at the time it was released.

See the full description and other details in the link above this one.

jpg HP Picture VA355 - HP-35s

The back plate of my HP-35s, an early model which was presented to me at the time it was released. Notice it doesn't seem to have a serial number engraved.

See the full description and other details in the link above this one.

jpg HP Picture VA410 - HP-41CX

This is my HP-41CX, the best classic version of the HP-41C, a revolutionary alphanumeric model every HP-calc fan craved for at the time of its release some 40 years ago. I certainly did so I sold my beloved HP-67 to buy one and did wonders with it (synthetics !), both for fun and for profit. The 41CX is depicted here with its mandatory (if power-hungry) card reader and both Advantage and PPC modules plugged in (alas, not seen from this angle). With it and a full 40-card holder or two you had enormous computing power on the go.

The CX, introduced in 1983, was essentially a 41C on steroids: built-in Quad Memory module, Extended-Functions/Extended-Memory module, Timer module, plus text editor and extra functions not available anywhere else, while leaving all 4 ports free for other uses (e.g.: Advantage module, PPC/HEPAX/ZENROM module, Card Reader and Printer, or additional Extended Memory). A Classic-Dream-Machine if there ever was one, with dozens upon dozens of application-specific modules, Solution Books and dedicated peripherals, both HP's and 3rd-party's.

Have a look at these articles I wrote where the HP-41C is featured (as well as some of my programs for it in the HP Calculator Programs section in this very site):

Long Live the Advantage ROM, (N-th degree Polynomial Fit program included)
Know Thy Foe: A New Contender, (comparing HP-41C vs. SHARP PC-1211, two 41C programs and 6 SHARP programs included)

jpg HP Picture VA411 - HP-41CX

This is my HP-41CX, the best classic version of the HP-41C, a revolutionary alphanumeric model every HP-calc fan craved for at the time of its release some 40 years ago.

See the full description and other details in the link above this one.

jpg HP Picture VA415 - HP-41CX

This is my HP-41CX, the best classic version of the HP-41C, a revolutionary alphanumeric model every HP-calc fan craved for at the time of its release some 40 years ago.

See the full description and other details in the links above this one.

jpg HP Picture VA419 - HP-41C Series leather case

This is a leather-like case for the HP-41 series models. It perfectly fits and allows for the card reader to be plugged in, with room to include some keyboard overlays while keeping the contents reasonably well protected against moderate impacts.

See the HP41CX's full description and other details in the links above this one.

jpg HP Picture VA420 - HP-42S

This is my HP-42S, the pinnacle of RPN calculators, a worthy successor to the HP-41C family which was intended to be completely compatible with it while adding incredible amounts of extra functionality such as full complex number support, matrices, solve, integrate, extended alphanumeric handling, named variables, graphics and menus. Add to that an enhanced, larger 2-line dot-matrix LCD display, much more RAM and faster speed and you have a real winner, a dream machine.

However at the last moment the product was badly maimed, probably to avoid cutting sales of the RPL models, and lost all kinds of I/O: no HP-IL, no card reader, no external storage, nothing but one-way communication with an I/R printer. It also lost all ports so no plug-in RAM and ROM modules, and its internal RAM was cut down from the possible 32 Kb to a mere 7 Kb. It was a real disaster for all of those people who, like me, didn't care at all for the RPL models and would rather have a very powerful, fast RPN programmable calculator as the HP-42S was intended to be from the start.

Alas, it wasn't to happen but it's still a fantastic, very worthwhile machine and, in emulated form (Free42) running on various operating systems, incredibly fast.

Have a look at the following article I wrote which extensively discuss and feature the HP42S:

Long Live the HP42S, (14-page article, includes a 'pro-looking' didactic program to solve the N-Queens puzzle in an NxN chessboard)

jpg HP Picture VA421 - HP-42S

This is my HP-42S, the pinnacle of RPN calculators, a worthy successor to the HP-41C family.

See the full description and other details in the link above this one.

jpg HP Picture VA710 - HP-71B

This is my very first HP-71B, which I got back in 1986 so it's now (2019) some 33 years-old and as you can see it's still absolutely as new and works flawlessly. Here it's depicted with a CMT 128 Kb RAM Memory Module plugged in the card reader port and perfectly matching the HP-71B's looks. I found the included card reader mostly useless for a number of reasons, so I eventually substituted it for the much more useful 128 Kb module, which can hold the equivalent of 200 magnetic cards at once, all of it instantly available.

Before getting this HP-71B I had been privy to a pre-production model before its release (it paid having friends at local HP headquarters !), which was lent to me for a weekend so that I could try it and see how I liked it. In a word, I found it awesome in the extreme, many many times faster than the HP-41C (though still 5 times slower than the much bigger and less powerful HP-75C), 16 Kb seemed like infinite RAM as compared to the HP-41C too (let alone when fitted with the 128 Kb module) and expandable to 512 Kb (in a handheld device !!), awesome HP-IL capabilities for interfacing with all kinds of peripherals and instruments at speeds many time faster than (again!) the HP-41C, the best BASIC dialect you could dream of and incredibly powerful plug-in ROMs such as my all-time favorite, the Math ROM which provides unbeatable math capabilities, even surpassing the full-size PCs of the time.

Thus, I was in love with the HP-71B and as soon as it was released I convinced my boss to get one for me (I couldn't afford the expense) with card-reader and HP-IL module fitted-in, and I bought the Math ROM with my own money (expensive but it had top priority for me, I'd rather not eat). I wrote lots of software for it, both for profit and for fun (lots too !!) and in time got several more HP-71B, this time for peanuts as the second-hand market was flooded with thousands of them discarded by some UK Government agency, so you probably can get one cheap too. Also, there's a number of very good emulators for MS-DOS, Windows and Android, most for free, so you can try one if you want.

Have a look at the following articles I wrote which extensively discuss and feature the HP-71B:

Long Live the HP-71B, (full description and history, includes a Text Stereograms generator program)
HP-71B Modest Mater, (program to solve Mate-in-N chess problems)
HP-71B Math ROM Bakers Dozen (Vol. 1), (many tips and useful code snippets, first part)
HP-71B Math ROM Bakers Dozen (Vol. 2), ((many tips and useful code snippets, second part))
HP-71B Short and Sweet Sudoku Solver, (program to solve any Sudoku puzzle)
HP-71B Sudoku Solver Sublime Sequel, (enhancement to the program to solve any Sudoku puzzle)
HP-71B Sudoku Generator and Coach, (program to generate new Sudoku puzzles and coach you to manually solve any puzzle)
HP-71B Fantastic FOUR, (multiprecision multiplication using Fast Fourier Transforms)
HP-71B Minimax Polynomial Fit, (program to fit a set of data to the very best possible polynomial)
25 years of Othello, (program to play Othello versus the machine)
Small Fry - Primes Acounting, (routine to very quickly count primes on a given interval with excellent accuracy)
Small Fry - Let's Be Rational, (routine to convert reals to fractions and find their continued fracton form)
Boldly Going - Matrix Square Root, (routine to compute the square root of a given matrix)
Boldly Going - Identifying Constants, (program to find the symbolic expression which evaluates to a given numeric value, many applications)

jpg HP Picture VA711 - HP-71B

This is my very first HP-71B, which I got back in 1986 so it's now (2019) some 33 years-old and as you can see it's still absolutely as new and works flawlessly.

See the full description and other details in the link above this one.

jpg HP Picture VA713 - HP-71B

This is my very first HP-71B, depicted here with a 128 Kb CMT Memory Module plugged in the card reader port which, together with three 4K Memory Modules (not visible from this angle) makes for a whopping total of 156 Kb RAM as shown in the display. This much RAM allows for more than 100 sizable programs kept in memory at once, instantly available at all times, or you can use it to process enormous matrices (up to, say, 135x135 if real or 95x95 if complex) or arrays (up to nearly 20,000 real elements or 10,000 complex ones).

Nowadays we're used to have many Mb or even Gb available in a small handheld device but back in the middle 80's that much memory and processing power in a battery-powered handheld computer which you could use in the middle of nowhere was absolutely unheard of, a worldwide first. Most people couldn't afford the expense so it made little news but a lot of professionals were delighted in the extreme and literally jumped at the opportunity to get it no matter the cost.

Actually, I knew one of these people, who bought several HP-71B (one for actual use and the others as spares, just in case), fitted one with more than 200 Kb of RAM, Math ROM, HP-IL ROM and tape drive and went out to the mountains and other difficult and isolated places whatever the season to interface the HP-71B with a number of measuring devices and take many thousands of measurements on location, to later analyze the gathered data at home and conduct very complex geophysical studies of the terrain. He was paid well enough that the cost of the HP-71B and peripherals was negligible in comparison, their acquisition really paid off.

See the full description of the HP-71B proper and other details in the link above.

jpg HP Picture VA714 - HP-71B

This is my very first HP-71B, and here you can see the four frontal ports with three 4K Memory Modules and the Math ROM plugged in. The memory modules, which add 12 Kb to the built-in 16 Kb of RAM, plus the (not visible from this angle) 128 Kb CMT Memory Module plugged in the card reader port, makes for a whopping total of 156 Kb RAM which you could increase even further by simply plugging in third-party 32 Kb memory modules instead of the 4 Kb HP ones depicted here.

Add to that the awesome capabilities the Math ROM provides (complex variables and matrices, complex arithmetic and functions, full matrix operations, Hyperbolic and Gamma functions, Integrate, Solve, Fast Fourier Transform, etc.) and you have the most advanced mathematical and processing capabilities on the go for any device of its time.

See the full description and other details in the link above.

jpg HP Picture VA719 - HP-71B leather case

This is a leather-like case for the HP-71B. It perfectly fits, with room to include the Quick Reference Guide and/or some keyboard overlays, and keeps the machine well protected against falls to the floor and impacts, but it has a terrible flaw in the (very) long run: after 20 or 30 years elapse the black mesh which lines the interior will disintegrate into a fine black powder that gets into all places: the LCD, the keyboard, the ports, inside the machine itself. The case can be recovered by thoroughly washing it till there are no traces of the black powder but the process of cleaning the HP-71B, while quite possible, is cumbersome and very time-consuming. The black powder doesn't seem to harm the machine, though.

If you've got one or more HP-71B insides these cases right now, you'd do well to inspect them carefully, and either store them out of the cases or place them inside hermetically sealed plastic bags inside the cases, to prevent the eventual disintegration's nasty effects.

COPYRIGHT NOTICE

These articles, programs, pictures, their descriptions and other materials created by me are (c) Valentin Albillo, and can be used freely for non-profit purposes as long as (1) the contents aren't modified in any way and (2) the copyright is acknowledged.

In plain words, you can download them and use them for non-profit purposes but do not include them in any media and/or site for which you're asking money, do not tamper with their contents and do not say or imply that you created them or that you don't know who created them, you must always give due credit to the copyright holder (that's me).