I've been enthralled with calculators since I played with one of the first pocket ones around 1972. They strengthened an already strong interest in math and taught me my first lessons in programming (I think my first actual programming experience was on a Compucorp, card reader and all, at school). Over the years, I've built a decent little collection. Some work, some don't. Some were bought to use, some acquired as collectibles. They are arranged in rough chronological production order. Don't take any of the data here as gospel. There are some approximated entries. If you can correct anything, let me know. Click on the thumbnail to get a larger image. Costs are in Canadian dollars. The "Forensic #" is a quick test to gauge the accuracy of the trig algorithms, the number of internal digits, and sometimes even the chip (set). The ideal result is 9. Check the site for more info (a couple of my results for nonworking units were taken from this site). The "69!" entry (get your mind out of the gutter) gives the time to calculate the factorial of 69. Last updated July 29, 2004. Click here to see a calculator book published in the UK in 1976 and republished by Coles Bookstore (Canada) in 1980. Click here to see a TI calculator book from 1978. 
Manufacturer Wang Labs 
Model LOCI2 (2A) 
Mfg. Date 1967 (s/n 3059) 
Accession Date ~1982 
Orig. Cost ~$3000 
Batteries 
Made in USA 

Display Nixie tubes 
Programming 80 steps (1 per keystroke), punched card 
Digits (guards) 10 
Forensic # 
69! 
Fractions 

Stats 
Nondecimal 
Memory 16, continuous (magnetic core) 
Conversions 

Comments A breakthrough calculator, this has a logantilogcomputing circuit at its heart. Therefore, multiplication and division are done internally as logaddantilog! Of course, this enables the relatively simple inclusion of functions like square and squareroot in addition to log and antilog. Circuitry is entirely discrete transistor (over 1,200); not a single IC. There is no program memory per se. Instead, the card reader has a contact for every possible hole position, and the card itself becomes a ROM! Very cool. Here are the manuals. 
Manufacturer Rapid Data Systems & Equipment Ltd. 
Model Rapidman 800 
Mfg. Date 1972 (s/n 122762) 
Accession Date Apr 2004 
Orig. Cost $100? ($400!?) 
Batteries 9V 
Made in Canada 

Display LED 
Programming 
Digits (guards) 6.2/8.2 
Forensic # 
69! 
Fractions 

Stats 
Nondecimal 
Memory 
Conversions 

Comments One of the earliest readily available machines, I think this might be the first calc I ever had a chance to sit and play with. Odd olive/khaki colour, I think it also came in black. It's a bit of a chore to use. You have to clear it before doing a +/ calculation or else the previous result will get used in an RPNish manner. In fact, doing addition and subtraction is just like RPN, which is also how many mechanical adding machines worked I guess. See the instructions on the back. The keys have a cool feel, with the numbers being recessed about 1mm. The display is fixed at two decimal places, but, you can use numbers >999999.99 (only millionaires would need to use such numbers, and there were fewer of them in 1972). When you exceed the display's capacity, the indicator to the right of the display comes on, indicating 1 or 2 undisplayed MSDs. When you're finished, divide by 100 to see the integer part. Overflow beyond 8.2 and you see 0 0 0.0.0.0.0.0. 
Manufacturer Sharp 
Model Elsi Mate EL120 
Mfg. Date 1973 
Accession Date Mar 2004 
Orig. Cost 
Batteries 3 AA 
Made in Japan 

Display Green VFD 
Programming 
Digits (guards) 9.3 (3 physical) 
Forensic # 
69! 
Fractions 

Stats 
Nondecimal 
Memory 
Conversions 

Comments The weirdest calc I've ever known. The button on the side increments the display by 1, like a person counter clicky thing. On top of that, the display is only 3 digits! If the number is longer than this, the display flashes between groups of digits, either automatically or manually. Up to 4 groups might be displayed  3 to the left of the decimal, 1 to the right. "Comma" graphics indicate which group is showing. Click here to see an animation of the display in auto mode. The build quality is quite rugged, and there's a cm scale molded into the back. Maybe this was meant for shop use??? Inventory taking?? 
Manufacturer Texas Instruments 
Model SR56 
Mfg. Date 1976 
Accession Date Jan 1977 
Orig. Cost $200 
Batteries 3 AA NiCd in cartridge 
Made in USA 

Display LED 
Programming 100 steps (1 per keystroke), volatile 
Digits (guards) 10+2 (23) 
Forensic # 9.000004661314 
69! n/a 
Fractions 

Stats basic 
Nondecimal 
Memory 10, volatile 
Conversions 

Comments A classic!!! I got lots of early programming experience on this. A great feeling calc. Best thing TI ever did! Can be mated to the PC100 thermal printer. Interesting  a slide switch for degree/grad selection, but a key command to switch to radians. Click here to see a program sheet for my SR56 pièce de résistance, a TugofWar game. Here's the back. And check out the nice manuals. 
Manufacturer Commodore 
Model PR100 
Mfg. Date 1978 
Accession Date 
Orig. Cost $70 
Batteries 3 AA NiCd fixed 
Made in England 

Display LED 
Programming 72 steps (1 per keystroke) 
Digits (guards) 8+2 (2) 
Forensic # 9.14705679 (12sec) 
69! 1.5s 
Fractions 

Stats 1var, P&C, LR 
Nondecimal 
Memory 10 
Conversions deg/rad, R/P, H/HMS, metric (4), cartesian/spherical! 

Comments Cute display has exponent digits smaller than mantissa. A surprisingly sophisticated machine for the time and price. Here's a friend's working unit. And with manuals. 
Manufacturer Nixdorf 
Model LK3000 
Mfg. Date 1980 (cartridge 1979) 
Accession Date 2000 
Orig. Cost $170 
Batteries 4 AA NiCd fixed 
Made in Malaysia 

Display 16 chr. alphanumeric LED (14segment) 
Programming 
Digits (guards) 7 or 8 
Forensic # 
69! 
Fractions 

Stats 
Nondecimal 
Memory 1 
Conversions Language!, metric, currency 

Comments A language translator with calculator functionality. I have the English/Polish module. To do calculations, you actually need a separate calculator module. There wasn't enough ROM space to combine calc and language! Modules were also available with PDA or database functionality as well as one containing 1980 Olympics results! Bet that one sold well. Oddly, the module itself contains not only the ROM, but the processor too (a Mostek 3870 microcontroller (Fairchild F8 core)). The display is comprised of four "intelligent" alphanumeric modules. Although I got the unit fixed up enough to power up, the keyboard connector is broken, so for now, I don't know any more about its functionality. Display goes into powersaving mode after ~20s. A 2s exposure is shown in the picture. Here's the unit saying something else. There's a bad display connection too, as the words and powersave display aren't quite "right". 
Manufacturer HewlettPackard 
Model HP85 
Mfg. Date 1980 
Accession Date Apr 2004 
Orig. Cost ~$4000 
Batteries 
Made in USA 

Display CRT, 32x16 character, 256x192 graphics 
Programming BASIC, 14K RAM 
Digits (guards) 12+3 (0) 
Forensic # 8.99999864267 (0.3sec) 
69! 0.5s, as a program! 
Fractions 

Stats 
Nondecimal 
Memory 
Conversions 

Comments More a computer than a calc, it's here because it's HP, and because it can be used as a calc, simply by entering expressions directly. Also, the processor architecture and speed lean towards calculatortype designs. Although the processor clock is only 613kHz, the architecture is streamlined for math and is a bit RISClike. For example, the operation r1=r1+r2 takes one clock (well, four phases of one clock, so you might say the clock is actually 2.452MHz). There are 64 registers. It appears to run significantly faster than a contemporary 8080 or Z80 system. 64line history. Amazingly high integration for 1980, the entire machine consists of 11 LSI chips that do everything  processor, ROMs, keyboard, I/O, video, tape drive, printer. There is essentially NO digital support circuitry. Most of the remaining circuitry is for power and the CRT. Eight 16Kb DRAMs, plus four more for video memory. Dynamic range of 10^+/499. This example has two plugin modules, each providing an HPIB (GPIB) interface. An HP page about it. And another. 
Manufacturer HewlettPackard 
Model HP15C 
Mfg. Date 1984 
Accession Date Sept 1984 
Orig. Cost $165 
Batteries 3 LR44 
Made in USA 

Display LCD 
Programming about 300 steps with 21 memregs 
Digits (guards) 10/7+2 (0) 
Forensic # 9.000417403 (5sec) 
69! 0.75s 
Fractions 

Stats 1var, P&C, LR 
Nondecimal 
Memory 67 max (no pgm mem) 
Conversions deg/rad, R/P, H/HMS 

Comments One of the best calculators ever made  by anyone. Shows well even on its 20th birthday (amazingly, the 15's sister calc, the HP12C Financial, is still being made after over 20 years! Quality never goes out of fashion). RPN of course. Program/register memory tradeoff completely under user control. The "C" in HP15C really means continuous. Even the display is held when powered down. Oddest attribute: No normal floating decimal! Easy enough to get used to, and it's always possible to view the full 10digit mantissa with a keystroke. Automatic 1000s separators (commas) can be changed to decimal points (decimal becomes comma). I tend to keep it in sci/eng mode with a comma decimal... Original batteries lasted for >12 years. Nuclear? Claims to fame: Complex numbers and matrices. Full implementations  all relevant functions work in complex mode, matrices can be complex. Computes integrals, roots. Does noninteger factorials! Takes a bit over 2 seconds regardless of the argument. Flags and full range of comparisons in program mode  more than visible on the front panel. Iregister allows indirection with branching, register and flag addressing, and other functions. Painless program editing  memory automatically shifts to make room or close gaps. Click here to see a couple of simple programs. Nice manuals. There's even a site dedicated to the 15 and to bringing it back into production! 
Manufacturer Casio 
Model fx451 
Mfg. Date 1985 
Accession Date Feb 1986 
Orig. Cost $36 
Batteries none 
Made in Japan 

Display LCD 
Programming 
Digits (guards) 10+2 (1) 
Forensic # 9.0000157179 
69! 1.25s1.75s depending on light 
Fractions yes, can store in mem and do 4func math 

Stats 1var 
Nondecimal base 2/8/16, logic ops 
Memory 1 
Conversions R/P, H/HMS, metric (8) 

Comments Fully solar  no battery. I also owned the predecessor to this, the fx450. When the 451 came out, featureitis compelled me to buy it  it had added metric conversions and four more constants! I sold my 450. In some ways though, I preferred the 450. It felt a bit more solid  the foldout keyboard was significantly thicker and stronger. Oh well, both nice machines. One of, if not the first to include builtin physical constants (13 (9 on the 450)). The first I'm pretty sure to combine solar, constants, fractions, and logical ops (and metric conversions) in one machine, and virtually unrivalled to this day! (well, maybe not) The Engineering mode keys are neat. Using them, you can bounce the decimal around in jumps of 3, either way, in case you prefer microfarads to nanofarads for instance. A rare instance of inverse trig functions being available in a single keystroke. Apparently, the museum's example is a rarer version with a larger solar cell. 
Manufacturer HewlettPackard 
Model HP6S (Solar) 
Mfg. Date ~2000 
Accession Date Mar 2001 
Orig. Cost $10 ($15 solar) 
Batteries 2 LR43 (1 solar) 
Made in China 

Display LCD 
Programming 
Digits (guards) 10+2 (2) 
Forensic # 8.99999863704 
69! 0.25s (nonsolar), 1.5s (solar) 
Fractions yes, can store in mem and do 4func math 

Stats 1var 
Nondecimal base 2/8/16, logic ops 
Memory 1 
Conversions D/R/G, R/P, H/HMS 

Comments Funny  the two versions of this calc are both called 6S. You'd think that moniker would be reserved for the solar. This model is actually made by Chinese company Karce. I don't know if HP had a hand in the design, or if they have simply taken it asis and rebranded it. I guess it's their way of establishing a presence in the scientific bottomend. Not RPN! Note that the Aurex SC108 is also a Karce rebrand and identical in function to the HP! The odd thing about the solar  there's no power switch! It's always on. I try to keep it wellilluminated, leaving the top of the calc sticking out of its pouch, so as to maximize battery life. The AC button kinda behaves like a power switch, doing a full reset. Continuous memory, as long as you don't hit that button! Yet, the nonsolar is continuous for memory and modes. Interesting that the 2cell nonsolar is significantly faster than the 1cell solar, though the solar does speed up in bright light. Really! Small exponent digits on solar only. The nonsolar is a bit thicker and more sturdy than the solar! Its blue colour sure makes it hard to read the legends. It's also better shielded. The solar has an internal LED! I can only guess this acts as an OVP in case the 4section solar battery puts out too much juice! 
Notes: LR44 aka A76 aka AG13 L1131 aka G10 LR43, LR621, 2025, 2032, 2325, 2335 Watch out for Chinese button cells. The quality of most over the last few years has been abysmal. I've seen store displays of cheap trinkets where over half the batteries were corroded! 