Commodore DAC-612 from 1969: Inside and Out

We take a look at a mostly-but-not-completely functional Commodore DAC-612 desktop calculator based upon the Casio 122 first produced in Japan in 1969; this particular unit was likely made in 1970. It uses Elfin display tubes and many components from a family of parts from NEC and Hitachi.
Excellent page from Brent Hilpert about the Commodore DAC-612: madrona.ca/e/eec/calcs/Commodo...
Early Electronic Calculator Technology Reference: madrona.ca/e/eec/index.html
Madrona Grove: madrona.ca/
To support 8-Bit Show And Tell:
Become a patron: / 8bitshowandtell
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1962 Commodore Report: archive.org/details/commodore...
Elfin tube Radio Electronics article: www.decodesystems.com/re-elfin...
Japanese power connectors: www.zimmers.net/commie/docs/cb...
Casio 122 site: casio.ledudu.com/pockets.asp?...
Canonical List of Commodore Products: www.zimmers.net/commie/docs/cb...
Philco SC1772 shift registers: ​​madrona.ca/e/eec/ics/shiftreg....
Adrian's Digital Basement 1970s Towel shown here: • AT&T Unix PC 7300 Mode...
Index:
0:00 Mini Commodore History
1:00 A tour around the DAC-612
2:29 About the AC power connector 163 (not quite)
3:54 Casio 122
4:33 DAC-612: What does it mean? Canonical List of Commodore Products
5:20 Power up: Odd Zeroes
6:30 Doing some calculations: Addition, Subtraction
7:30 Multiplication and Division: No longer working
9:43 Decimals & Rounding
12:10 GT (Grand Total?) and double plus
13:42 1970s Towel: Thanks Richard Pepper
14:04 Undersides
15:11 Inside: first look
16:20 Display board: Elfin tubes
17:17 Keyboard
18:23 Power supply & removing the top logic board
20:03 Examining the boards
21:16 Integrated Circuits in a can & JMOS
23:03 Philco SC1772: 48-bit shift registers
24:25 A few other JMOS ICs - madrona.ca
25:37 Thanks!

[@RetroAdrianBlack]

I almost fell out of my chair when you broke out the 70s towel!!! That is so funny and so awesome!! Perfect to use on that wood grain calculator. :-) Welcome to the club!

[@gklinger]

Begun the 70s towel wars have.

[@mal2ksc]

I will never complain about your towel again.

[@SteveGuidi]

My parents still have towels that match this trending style adopted by the KZbin retro electronics afficionados. Could this is be a Canadian thing? I'll be visiting them next month in Toronto -- maybe I'll sneak one out of the house. I'll have to hide it from my wife though as she'll throw it out on sight!

[@gklinger]

@@SteveGuidi I've seen your name on Facebook and never realized you were from Toronto. When are you going to be visiting? Maybe you can attend the World of Commodore...

[@reppepper]

Hey, Robin, are you going to give me my towel back, or will it have permanent role in your videos from now on?

[@user-ij5sm2wk7y]

The underside of the keypad when you showed it has the numbers "45 5 2" (or similar) stamped in it in white. This is for the Japanese Showa year 45, so that dates the unit to May, 1970.

[@8_Bit]

Nice catch, thanks!

[@antoniomaglione4101]

Japan now is in the Reiwa era, begun on 1 May 2019.

[@watchmakerful]

Half-height zeroes were common in calculators that weren't able to suppress leading zeroes.

[@NozomuYume]

When you think about it, it's a good idea, as it lets you quickly visually see where your value starts.

[@denormative]

@@NozomuYume I would imagine it would also help differentiate between 8 and 0 much clearer.

[@QuantumScratcher]

To this day, some people still write 100 like 1oo.

[@lucasrem]

we already used the Japanese models, flooding point unit needed, dividing Zero! E.W. Dystra was faster than these machines, that was EPIC!

[@haroldlane4647]

Try holding an AM radio next to the DAC-612 while it's operating. You might hear some cool sounds. I first heard (read) in an electronics hobbyist mag (possibly Radio-Electronics) from the 80s (?) that you could use a digital calculator to test your car's AM antenna. Most calcs of the day had LED displays and 9v batteries. My high school TI-30 or 35 made the sweetest calculation sounds when it paused to calculate a trig function. An older general purpose calc made it's own unique noises on this radio: a flashing error display made a good fast-beat klaxon sound and the buzz was louder with each digit that was lit. Would love to see how the DAC-612 sounds

[@lucasrem]

Are you new to electronics, frequencies and waves, early computers, you can hear what they do!

[@CanadianRetroThings]

The adding/subtracting is working as an accounting adding machine does, when you put in a number you then hit the key that says wether it is a negative or positive number. This means, rather than adding and subtracting you are totalling a list of negative and positive numbers (it makes more sense when you have a ledger with a list of 40 or 50 numbers to total up)

[@csbruce]

So, it's a "Negate And Sum" function.

[@ropersonline]

Would it also work to press 500 [-=] 400 [+=] ?

[@CanadianRetroThings]

@@ropersonline You would get -100 as the answer, you are making a list of numbers, in your example you are saying 500 is a negative number, 400 is a positive number.

[@marknesselhaus4376]

Thank you for that info as I was given a old 1970 ish calculator that acts the same way and I had been scratching my head over the results. Now it all makes sense :-)

[@CamdenBloke]

In the early 2000s I worked at a gas station and for taking inventory of cigarettes (a daily task) there was this funky calculator that had buttons like that and behaved unpredictably when I tried to use it. I was studying mathematics in university at the time and was familiar with both algebraic and RPN inputs. It took me a while to figure out how to use it. A coworker who was about 20 years older than me didn't understand why I was confused by the calculator and said it was "just a regular calculator".

[@MicrobyteAlan]

Very interesting and well presented. A trip down memory lane, I started as a computer engineer in 1969.

[@DaveF.]

That's really interesting - a lot of the odd look and feel of how this behaves - the display of all zero's when turned on; the fixed position of the decimal point once you start using it - all make perfect sense if you're used to a mechanical adding machine.

[@richpickings2845]

LGR has to be drooling over this beautiful wood grain beauty.

[@ChaseMC215]

And The 8-Bit Guy is drooling over the Commodore brand

[@TheStuffMade]

Thanks for taking it apart, nice to have a look inside. No wonder these calculators were very expensive back in the day with the complexity. I can imagine many man hours went into just assembling a single board with all the wires and everything, and probably a large percentage didn't work after assembly and had to be tested and repaired before ending up in a calculator. Cheers, Jake

[@lwilton]

While there would certainly be a rework area for things that didn't pass QC, the failure rate was probably a lot lower than you are imagining. I'd bet it was around 1% or so, or they would not have been able to afford to make these. The biggest failure area would probably have been with mis-connected jumper wires. But those wires would have all been pre-cut and stripped to length, and the production line would have been arranged so that things were done in a specific order that made it relatively hard to mess up and connect to a wrong via.

[@domramsey]

I have a much earlier Commodore mechanical adding machine and I love it. It's fascinating seeing the mechanism in action when you press keys. None of this new-fangled "electric" stuff.

[@MichaelDoornbos]

I have several mid 70s calculators, but nothing this old. So awesome to see this in depth. 5:00 magic smoke can usually be put back in if you let it out I love this calculator stuff, but the song at the end is the best part.

[@katho8472]

Indeed! Where does the song come from? What did I miss? I mean I can hear it's Robin singing, but except that...

[@AureliusR]

@@katho8472 it's his band The Bedford Level Experiment!

[@JustWasted3HoursHere]

Ah, I miss woodgrain on electronic devices like this (and the Atari 2600) back in the day.

[@charlesbaldo]

The multiplication and division issues makes sense for the challenges at the time for hardware and coding. I remember a class I took in 1978 doing assembly language on an IBM 370 the school had. Our final exam was to write multiplication and division routines, it was all series of adds or subtractions with register shifts. Which is exactly what is happening here.

[@MurderMostFowl]

Those traces at 20:42 look like a river flowing. It’s beautiful!

[@lwilton]

All laid out by hand. Before any software to do PC board layout.

[@JustWasted3HoursHere]

Within ten years after this calculator came out these things have already been MASSIVELY simplified in their circuitry. Modern calculators have essentially reduced everything to a single tiny chip.

[@greatquux]

Yeah in fact just yesterday I read it’s the 50th anniversary of the Intel 4004 which was designed for a calculator!

[@megatesla]

The first single chip calculator was released early in 1971. So about 2 years, not 10 years...

[@JustWasted3HoursHere]

@@megatesla I said _within_ ten years.

[@androo4519]

A lovely old calculator. The number of components is incredible. Those half-height zeros are very Casio. They used them on VFD models too until maybe 1975. You see them on the Sperry-Remington calculators that are based on Casio models.

[@user-bu9nx4ot2u]

Thanks for your time and effort in keeping 8-bits alive!

[@DrDavesDiversions]

Fascinating, Robin - thanks for the tour!

[@RonLauzon]

When researching some Sperry calculators that I have, the reason for the half height zero is so if there's a segment failure, it will be more noticeable.

[@DaveEtchells]

This reminds me of a college digital electronics course I took in 1974, where we designed an 8-digit calculator over the course of the lecture series. The prof walked the class through the design step by step, drawing implementation suggestions for the logic from the students and discussing the relative merits before choosing one and proceeding. His TA had an assortment of 7400 TTL logic chips that he used to wire-up the evolving circuitry on a breadboard as we went. The whole thing was built from discreet logic and used a serial ALU and shift registers just as in this Commodore design. By the end of the semester we had an ungodly sprawl across 2-3 square feet of breadboard panels, but it was a working 4-function calculator 👍😁

[@8_Bit]

Sounds like an excellent subject for a course, lots of practical and theory together.

[@DaveEtchells]

@@8_Bit It was very effective, we really got a good feel for how to put together digital circuits to actually do things!

[@scality4309]

Your channel is a gem! ❤️✌️

[@nickyborrisino]

Absolutely gorgeous trace design on the top board.

[@lonewolf31337]

I just came across your Instagram and had to come check out the KZbin channel. I’m glad I did awesome videos

[@ag3ntorange164]

Beautiful. I want!! Thank you for letting us peer inside. Great video!

[@TomaszWiszkowski]

Wow this power cable connector looks like trouble when the cable is plugged on the other end... Beautiful piece of vintage equipment. Thank you for this video!

[@westelaudio943]

Yes, making things "idiot proof" was not much of a concern back then.

[@video99couk]

Makes my 1975 Rockwell pocket calculator look like something from another planet. A lot of progress in a few years. Of course most "newer" calculators don't use a CPU as such, it's just a much more integrated "system on a chip" design.

[@naderhumood1199]

Thank you v much Sir, Great video. Lovely machine, and lovely past.

[@ryballs4569]

Thanks Robin for the interesting video and cool song at the end, where can we find the full version?

[@kins749]

Absolutely fascinating!

[@reiner0609]

I wonder if the 7/32 nuts aren't just regular M3 metric as 7/32 is awfully close to the 5.5 Millimeter of a M3 nut.

[@8_Bit]

I'm curious about this as well. I know Japan has been metric for a very long time but they would still use other units in manufacturing at least in some industries, especially 50+ years ago.

[@lwilton]

@@8_Bit I'm betting that it was 5.5mm, but you are right, they did use SAE parts on things for the American market in those days. However, by the 1960s (really by WW II, when "national standard" parts sizes came into existence) the odd 32nds nut and bar stock sizes that had been common in the first half of the century had been largely dropped in almost everything except automotive ignition parts. That makes it much more likely that this is really metric.

[@lwilton]

@Electronic Adventures Well, you are almost correct _today_. In the 1960s you would have been quite incorrect, and that is when this was built. Thus the size was a legitimate question.

[@ByWire-yk8eh]

Today, there are only three countries that don't use the metric system: Miramar, Liberia, and the USA. Now, that's Making America Great Again!

[@westelaudio943]

@@ByWire-yk8eh That's not strictly true. Many countries still use imperial or other pre-metric units for many things, even though they mainly use metric. Thread sizes, wheel diameters, etc. And it's just not worth making truck loads of tools, parts and machinery obsolete just because some people don't like fractions. The metric train for the US has departed... 100 years ago.

[@Zhixalom]

Such gorgeous machines ❤️ The "strange" way the DAC-612 adds and subtracts bears quite a lot of resemblance to book keeping. You know like in the debiting and crediting kind of mindset... so really not that strange anyway.

[@dwindeyer]

I imagine the primary use for calculators at this time was balancing ledgers so the design choices strike me as completely intentional

[@Zhixalom]

@@dwindeyer Precisely what I was thinking 😉

[@Breakfast_of_Champions]

Yes! The 1960s towel! Grandpa Calc rarely felt so good in his life🤩

[@kemi242]

Clint of LGR would approve the brown plastic/woodgrain design. :)

[@merykjenkins3274]

I wonder if the leading zeros are to keep the display warm? I certainly hope that the calculator can be repaired and restored, what a great piece! I wonder if I can get to-5 package ic's for my c64? That would look awesome inside! Thanks again Robin!

[@DaveF.]

It's also exactly how a mechanical calculator would display it's output - I wouldn't be surprised if that was also a factor is setting it up that way.

[@DenizTurkmen]

I think so. Also if it's blank we wouldn't know if it's out or really blank.

[@mjh5437]

@@DenizTurkmen Good point!

[@Loenne555]

Love those classic mainboards with their handdrawn traces. Piece of art.

[@Bubu567]

DAC = Desktop Adding Calculator. That is a name used by casio. Is this a rebadge? Pretty sure the half height 0 was simply a simplification of the routing and reduced the number of components, but I could be wrong.

[@Dedicatedtolivinginthepast]

Its fascinating seeing really complicated electronics from over 50 years ago!

[@tiikoni8742]

6:10 Since it is filling leading digits with zeros also, could reason for half size zero be just to make it easier to see from where actual number begins.

[@1337Shockwav3]

Half size zeros were actually quite common back then. I can't recall the exact model but I've seen calculators with VFD displays showing the same behaviour. I _think_ it was from Sharp and had slightly more natural looking numbers. EDIT: Google turned up "Facit 1128" with a very similar display to the one I've encountered. Half size zeros there.

[@markboulton954]

@@1337Shockwav3 Also many books (especially financial ones) of that era were printed in what was called "ranging" type. A zero was a small circle like a lower-case 'o', a number 1 was like a small 'I' with serifs, the number 2 was also half-height, numbers 3, 4 and 5 descended below the baseline, 6 ascended, 7 descended, 8 ascended and 9 descended. There must have been legibility reasons for this, but it fell out of style in the early 70s and was replaced by "non-ranging type" in which all digits were full height with no ascenders or descenders. See: upload.wikimedia.org/wikipedia/commons/2/20/Poliphilus_468.png

[@markboulton954]

@@ButterfatFarms I think it derives from the Arabic way of writing numerals which is where our number system comes from. Most numerals ended in a downward stroke of some kind where the pen nib is lifted from the page leaving a trail of ink.

[@benanderson89]

My complete wild guess on the multiplication bug is that some kind of memory switching circuit similar to what an LS series chip in an 8-bit does. A line or lines is being held high or low, and the multiplication button must send the equivalent of a rotate command to the display memory and when the value falls off the end of the display, whatever handles that must finally pull the rouge lines high or low along with the working ones to finally let the logic circuit perform the calculation. Multiplication on a fundamental level is also a multiplication to a computer, so it's no surprise it also affects division.

[@diegoprat3709]

Great video!!

[@brightquark]

First thing that jumped out at me was those pins on that power cable appear to be flush with the external plastic so possible to brush against a live conductor when not plugged in to the calculator. Id be very careful when handling that cable. It just goes to show the many silent safety features in modern plugs we just take for granted now

[@greendryerlint]

You can really tell the age too by the cylindrical can germanium transistors on the board. And the can ICs of course. Back from the days when building PCBs of this complexity was a labor-intensive art. I'm sure these were hand-assembled.

[@moconnell663]

They were hand-stuffed, but wave- or selective-soldered.

[@tookitogo]

@@moconnell663 Automatic insertion was actually already available by 1970, when this thing was likely assembled (since the oldest component date found was at the very end of 1969) so it’s possible that most of the components were placed by machine. The wiring and connectors would definitely have been placed by hand though.

[@moconnell663]

@@tookitogo that's interesting! I thought the squeezing of IC legs to get them to fit in the PCB locations would have required human hands. My work just discontinued our very last all thru-hole assembly (one of those products that people just refuse to stop buying). I'll have to check with our assembly house to see how they've been doing it.

[@neilloughran4437]

Beautiful!

[@Vallee152]

I would like to see some of TI's old programmable calculators, those ones with cards you can store programs on

[@thorro3]

Very cool. I remember my parents using a mechanical adding machine with a paper "display" even in early 80s.

[@fischX]

DAC Digital analog calculator - a Casio thing back in the day. Probably also the reason why the thing freaks out a little - it uses discrete components for calculation that give out a voltage that then gets converted to digital. It's cheap it's fast, it gives you a result that is correctish

[@jamesbennettmusic]

The NEC can said week 2 of 1970 so it must be right on the turn of the decade!

[@rubusroo68]

beautiful

[@jpcompton]

8:08 Why did you cut the video just before we saw the overflow?!

[@nicholastotoro7721]

Kill screen coming… 🤣

[@antoniomaglione4101]

Incredible. The board with all that wires should have been a four layers type. The keyboard is made to last forever. The shift registers, multiple gates and half adders are used instead of a CPU and contains all transit memory. The 4004 for the Busicom was still to be invented in 1969. I don't know the uPD serialization used by NEC, but at that time we used RTL logic, which preceeded DTL and TTL. In those years the americans invented the 2N3866 transistor, able to produce few watts at UHF frequencies in a TO39 case, and powered the radar in the lunar lander. Eroic times for technology. Thanks for the video, I enjoyed the jump in the past...

[@lordanthrax2417]

The tracing! Man! Mindblowing! Would love to see the process of building everything from start to finish

[@lucasrem]

why you need that, the blue prints you need? making PCB's your hobby? Post it here, wee if it is anything people need to see here!

[@lordanthrax2417]

@@lucasrem i maybe did not express myself correctly cause english is not my native language,sorry. my point is that i am realy impressed of the handmade work that went into this. it feels like a lost art to me to build something like that and i get a weird satisfaction whenever i need to resolder stuff on my gaming consoles or fix a broken cables. i wont call myself someone with great soldering skill so this gets a massive respect from me. thanks

[@lordanthrax2417]

@@lucasrem i just want to see it cause i love it. its like watching someone making art.

[@ByWire-yk8eh]

I have a 1969 Friden Singer EC1113 calculator. It has 12 Nixie Tubes (Hitachi CD-71), and the logic technology is 108 Small-Scale PMOS IC's, Hitachi HD7xx-Series. It works fine, and I thougt it had a bug in the reset function. Reading up on it, I found out that the reset problem was a 'feature' and not a bug; They all worked that way.

[@logiciananimal]

Out of curiosity - how does this handle overflow (and divide by zero)?

[@MontieMongoose]

Wow that towel is very 70s.

[@lariveePhoto]

The keys sound really great

[@cpt_nordbart]

Curious Marc could probably safe this. They recently repaired an PS/2 main board with some interesting errors. They also did an interesting series about Apollo Computers like from the Space Program.

[@GrosvenorAudio]

Like the sound those keys make 👌

[@TheTarrMan]

When multiplication was working at 7:38 I noticed the "Sigma switch" was in the other position. I don't know if that's relevant to the issue.

[@SergiuszRoszczyk]

Thanks! Given the fact that YT filled advert blocks with music digital audio converters I know it has no clue about video contents itself 😀

[@nathanwoodruff9422]

Your multiplication is off because when you originally multiplied the switch was in the 5/4 cut position and now when you are multiplying the switch is in the OFF position.

[@gshingles]

The "C" in the part number might be for "Ceramic". I don't know if DIP came out of the gate as plastic, or when PDIP was introduced; I couldn't find any info on that (there's a reference in wikipedia to a 1979 study comparing the cost of the two). I tried scratching the screen to see what they felt and sounded like, but that didn't tell me anything,

[@lwilton]

DIPs were originally ceramic, but those were made of an upper and lower ceramic plate with hermetic sealing frit in between, like a sandwich. They were hermetically sealed, like the metal cans with the gold-plated leads. Plastic DIPs of the early era suffered from not being as well sealed, allowing some moisture ingress along the leads, which could lead to eventual chip failure. They also had problems with some of the plastic chemicals eventually breaking down the passivation layer on the die inside, corroding it or the leads, again killing the chip. The C in this case is separating the plastic DIP parts from the original parts, which were probably the metal can TO-5 (I think, at least TO-something) military grade parts. In TTL the letter N was often used for plastic parts.

[@tookitogo]

Most of those DIPs don’t look like ceramic, though. (The Hitachi chips are definitely ceramic, for reference.) I can’t be entirely sure without touching the chips, but the shapes and mold lines on the NEC chips look like plastic DIP.

[@youreperfectstudio4789]

Where do I hear the rest of that awesome song at the end?

[@cmuller1441]

With the small zeros, it's easier for your brain to ignore the leading zeros. Watching the video, it's obvious that this trick works well ...

[@martinhaub2602]

I love this kind of thing. This old technology is just fascinating! My old Singer/Friden desktop calculator with a CRT display and based on ECL logic still works, but I need someone more technologically literate to explain how it works.

[@lucasrem]

All you need a a display, or read the Pascal wheels! They all do the same thing!

[@dru1432]

The way this machine handles subtractions is... interesting. :)

[@ossianhaufe4671]

A really interesting device. It isn’t high integrated, is it? But nevertheless sophisticated more than I expected. I’m really impressed how you figured the issues out by trying some calculations. Could you fix it?

[@retrotechandelectronics]

The power cable looks like that of the connector of my old HP harmonic distortion analyser.

[@Gazdatronik]

My 1985 Panasonic does the same thing with the plus before minus subtraction. I used it daily for production tabulation and came to prefer it.

[@alpaykasal2902]

JMOS :) Those traces are crazy looking!

[@alpaykasal2902]

I'd love to hear stories about the process from the old timers designing and producing these boards

[@jakubkrcma]

😱The complexity! 😯

[@april7_]

Slightly amused 14:40 when you guide not to open wrong screws! How many of these have survived? I got only 2 models from 70's and one Texas Instruments model. Thanks for sharing these! That must have been an expensive one late 60's!

[@OtaconEmmerich]

I just noticed the NEC logo is stylized...I'm use to the more plain NEC font logo from the 80's and 90's.

[@Soulintent95]

Ive never seen an early calculator. Never really thought about it either. I always assumed calculators came after the computer and unless they were for business use and included a printer they were relatively small.

[@personalidol]

Any DAC-612 demoscene?

[@gaeshows1938]

nice!

[@berndeckenfels]

Fran would love those display tubes

[@WhatALoadOfTosca]

Hi Robin. What's the story with the Commodore Security badge?

[@8_Bit]

Hi! It's a reproduction of what the actual security guards at the Commodore plant in Pennsylvania had on their uniforms, made by my friend DLH who runs the excellent bombjack dot org website.

[@WhatALoadOfTosca]

@@8_Bit thanks Robin. I thought maybe you worked as security for them. Thank you.

[@atkelar]

I still think that half height zeros might be a design choice to make it visually easier to see zero from eight. As somebody mentioned, the leading zero suppression might have been a reason, but for financial stuff with commonly computed in thousand or million values it also might have added simplicity; I'm not aware of any specific meaning, but the "C" suffix on chips would be a good hint to the "ceramic" case as opposed to the "metal" one. I'm looking at a data sheet for a MC1496 now that also came in both versions and early chips seemed to have re-used the metal cans from transistors and gradually transitioned to the DIP packages we know. Sadly I might need an adapter for that old chip, cause I clearly suspect it to be broken in my device.

[@eekmeout]

It's beautiful to me

[@CallousCoder]

Lol yesterday I fixed an East German chess computer (video on my channel) and after I’d put it back together, I also saw a warning to unplug the device before opening it. Now obviously you always do it. But I found it funny that I’d not seen it until I had it fixed :)

[@awilliams1701]

yeah -24v is really unusual so it's pretty hard to replace. It's too bad it's not TTL if it was it would be easy to fix.

[@zigsym]

Hahhaa! It looks like it came as the matching free gift when Chevy Chase bought the "Family Truckster". Seriously though, great video of a beautiful vintage machine. Thank you.

[@ericcarabetta1161]

19:36 These ancient circuit traces on the brown circuit board look like worm tracks on a piece of wood and all the giant ICs are like pill bugs.

[@jms019]

Nice towel !

[@LilMalygos]

Great towel

[@VladoT]

It seems that those NEC chips are similar to the later TTL 74xxx family of logic chips.

[@iCQ_www.SPCL.tk_]

what a beauty... and a monster at the same time :-)

[@MD_il_microcanale]

you brought extremely erotic Commodore themed content! I love the Commodore DAC-612!

[@jaredloveless]

9:10 I've played with some old calculators and a lot of times they have unintentional features that are just bugs with how they coded these things

[@robertinobongiorno5148]

Nice calculator

[@MurderMostFowl]

“ I can’t decide if this is Hideous or beautiful” … my thoughts exactly. How wonderfully strange looking. Dignified yet ugly

[@scottl.1568]

Sweet...

[@SabretoothBarnacle]

$125! Quite a gamble for an 'untested' purchase!

[@8_Bit]

Pound for pound, component for component, woodgrain for... woodgrain (?) it was a bargain! In today's market I was surprised it didn't go for a lot more.

[@SabretoothBarnacle]

@@8_Bit I hope you can find someone who is willing to spend the time getting it running for you! Hopefully, after it is fixed you can demonstrate it again in all its glory?

[@rjhelms]

I wonder if "C" in the part numbers on the chips means "ceramic" - from a time when the most relevant distinction would be ceramic DIP vs metal can.

[@RonJohn63]

4:36 I posit "Digital Accumulator". 11:10 "Σ" is the math symbol for summation (which is what bookkeepers do a lot of).

[@AB-Prince]

my guess is that dac stands for desktop automatic calculator, due to replacing mechanical calculators which were a bit more manual

[@freddylq67]

I like that towel!

[@georgemaragos2378]

Hi - Early calculators added up a bit funny, but it was not quite reverse polish notation For example today calculators ( and mid 80's onwards ) you perform the addinf by the way you talk eg 1 + 2 = we get 3 the older machines were 1 + 2 + = we get 3 This was enter first number and then what do you do with it, enter second number then what to do eg add or subtract in a few companies i was given or had some of these calculators and i actually fond it frustrating and used my own - they were know as Plus Equals machines, they were fine if you learnt on it and never used the other style, but i was to young for that. Also later you had the sign change where you enter say 1 + 3 sign change to make it a negative 3 so the answer would be -2 The 5/4 is the rounding so it would round up on 5 and down on 4 sort of like converting to integer maths They way to think of it is like scamming interest payed 1.49 become 1 so you work out interest on $1 not $2 in this example you save 1/2 your payment - but bot very practical if you had say 123.44cents , it will become 123 - then you do the extra maths however - think of that 80's superman 2 movie and think of the input is all as cents, you cannot collect or pay a portion of a cent so it disappears These days the round is normal set to "floating" or do not round - same as excel where you showplay or show 2 decimals or whatever it takes Oh, the machine also had to perform less cycles to display the answer as it was not processing multiple calculations to show say 8 decimal places

[@Livinghighandwise]

Fascinating. I tried to find the original price of this calculator but failed. Does anyone know what this cost new back in 69?

[@ordinosaurs]

If you intend to repair it someday, maybe contacting Curious Marc might be helpful. He's already repaired invaluable electronic pieces from the era (Alto computer, HP equipment, and even an Apollo LEM computer !).