Comptometer Arithmetic

How to do the basic arithmetic (addition, subtraction, multiplication, division) on a Comptometer mechanical calculator.
For a look at all the features of this Super Totalizer Comptometer, see my other video:
• The Comptometer Super ...
You can find more information on my site:
www.jaapsch.net/mechcalc/

[@ParArdua]

Loved watching the women using these so fast in my office in the 70s. They never looked at the keyboard, always looking to their left where the cheques and receipts were, and always looking so relaxed. When the Wang computer was introduced in 85, they could not do it as quickly, so these were brought back for them. Thanks for the explanation.

[@usethenoodle]

My mother as a young girl was a Comptometer Operator in Chicago during WW-II when my father was in the Pacific fighting the Japanese. I bought one to keep on display in my home. My mom and dad are both gone now. They were great people.

[@ThePiquedPigeon]

One of the most pleasant sounding machines I've ever heard. All those clicking sounds are so nice and give the impression of a solid machine.

[@BokBarber]

It is, in fact, quite a solid machine. The metal linkages inside are so tight together that they look like they're in a woven pattern. These beasts are heavy.

[@BokBarber]

I've been training on a 12 column Model H Comptometer for fun, just to see how fast these are at basic arithmetic using the methods in the freely available Felt and Tarrant user manuals. Essentially just punching in the odd equation here and there, tallying up a few receipts a week, and using it instead of a computer calculator for quick math. The answer is that it's reasonably fast. Usably so. Not as fast as a digital calculator except in some niche cases, but still impressively fast for what it is. For addition, specifically addition of small dollar amounts, these things are lightning fast. In that specific context it's faster than running the same total on a 10 key calculator, but even with other types of numbers it's competitive; a well trained operator would probably beat the more modern machine at all addition. The best method I found is to use the touch method you showed, and work the columns lower order to higher order, 2 or 3 at a time so you don't get your fingering messed up. Multiplication is less fast since you have to look at the keys and chord your hands to effectively type the same number over and over. It's not as fast as using an electronic calculator, but significantly faster than doing the math on paper or in your head. It's only a second or two per multiplication for more simple numbers. It gets significantly slower the bigger the number gets, since the more fingers you're using the more careful you have to be with your presses, and eventually you reach a point where you have to enter the number in 2 parts... but even then it's reasonably fast. Subtraction is somewhere between multiplication and addition in speed once you know the rule. It's just the one press but you do have to think about it for a moment. Division is really not bad if you get used to the rules, and takes maybe 20 seconds to run the decimal places all the way to the right on a 12 column machine. You could calculate more precision by writing down the answer then clearing the register and continuing the division on the last remainder, which is a power that electronic calculators don't usually have but also makes everything take longer. Overall these are fun machines that are still usable if you're nerdy enough to practice on them. They're obviously not the most efficient means to an end for four function math anymore, but they do make running boring, tedious calculations slightly more interesting.

[@JAYGMART]

Oh loved this! I learned to use these machines when I was 17-18. Later worked in London as a temp and travelled to many businesses with my comptometer. So now I sell antiques and when one of these comes up at auction viewing it’s a blast to show other dealers how they work.

[@chrisnauta2467]

My mother in law said she was an operator on these machines back in the 60s. I had no idea what she was talking about. Now I am starting to understand this machine 👍

[@Nupawru]

Found one of these in my grandparents shed. Figured it couldn't do anything other than addition but you explained it perfectly

[@blueskye6372]

Did keypunch back in 70s for database entries. Went to business school took touch typing and shorthand later ended up as the Recording Secretary for Board meetings and then the IT Guy who installed the computer network trained staff DOS Prompt then ICON and Computer Mouse use. Those were the days.. 🙂👌

[@ct92404]

I just bought one of these. Mine is a Model J, from 1929. These antique machines are really cool - it amazes me that a purely mechanical device can do calculations! But doing subtractions would get so frustrating! I was playing around with mine today and I figured out how to do addition easily, but I still haven't gotten the hang of subtractions. This is nothing like a modern calculator, that's for sure!

[@jaapsch2]

Cool. I hope my video helps you out. On my website you can also find various instruction manuals for it in pdf form if you prefer things in writing. www.jaapsch.net/mechcalc/comptometer.htm#books

[@PopeLando]

ct92404 That's not quite true. To subtract on the comptometer you add the complement. Your calculator does the same. Your calculator cannot subtract. Neither can your smartphone, your desktop computer or Google's largest server. None of these computers are any more capable of subtracting numbers than that comptometer is. They all do it by adding complements.

[@robbiedart7422]

Thanks so much! I have my Grandma's old electronic comptometer and finally got chance to use it. Sadly a lot of the keys seem to be stuck in/be unresponsive... I would love to know to fix it. But the keys that do work are so satisfying! And it makes a fantastic whirring sound when plugged in If only I could do some maths on it!

[@ShamelesslyCreative]

I own several models of this machine and I even have the Comptometer trainer and trainer books, but this helped so much thank you for making this video. Appreciate it. My interest and collection is in calculators and adders before electricity ( after that I lose interest) and I also have a few very specific slide rules. Happy to find your channel. 🥰

[@AbdullahAwamleh]

Neat to see one of these in operation. The Felt and Tarrant factory is now loft condos in my neighborhood in Chicago.

[@windsofmarchjourneyperrytr2823]

Those old factories are solid buildings.

[@windsofmarchjourneyperrytr2823]

I was reading a paper my father kept from 1955! to see why he kept it to start with...they mention this machine and here i am.

[@michaelbauers8800]

I found it clear, but I am a computer programmer, and learned two's complement when I was 16 or 17, so it's built into my brain how complement math works.

[@art1339]

Subtraction, if you think about it, is a series of 9s compliments, with the exception of the “units” or “ones” digit, in which case that’s a ‘10s’. Because that 10 will carry to the tens digit (which is a 9 compliment) and that 9 compliment will then be a 10, carrying to the next when needed, etc... Easiest way I do subtraction is exactly what he said-small digits, metal bar pushed to the left of larger number, fill in blanks with little zeros (co digits). 43,856 - 3 for example You enter 43856 so it shows in register at bottom. Hold down metal fork to left of 4. You’re going to enter in one less than 3, remember, because of the 10 thing in the units place. All remaining digits are the proper 9s compliment, so you can’t forget about the ones with nothing, therefore: 43856 - 00002 (small numbers) will give you correct answer. Now when the number to subtract is a 9, there are no small 9s, so you skip it. 300 - 100 Hold down metal bar left of 3. Enter small 099, because one less of 100, but there isn’t any small 9s to enter! So just a zero In the hundreds place will give you your answer 😉

[@jessieyoung7546]

Well, way back in the 60's, I did some training on one of these machines,, and we had to hold use both our hands, but our fingers were sort of crossed over ,and held a a strange angle. And of course, you had to employ mental arithmetic as you went along.It really was quicker doing your sums on paper.

[@brianasbury8315]

That's old technology, but that's a really cool machine.

[@someonespadre]

The 9s complement applies to pinwheel type calculators too. On my Monroe I want to multiply 51.335 by 15.767. So I multiply by 16.000 then backwards .234 (the rightmost is always a 10 complement). The .234 is red numerals in the counter dial indicating backwards multiplication. Depending on the calculation this can save a lot of cranking. The answer is 809.399 either directly or using backwards cranking as detailed here. According to my testing it is required to do the 16 first, then 2 3 4 working backwards. It doesn't work starting from the right as is done in regular multiplication. A more dramatic example is 525 x 999. Crank 1 000 then carriage all the way to the left and crank one backwards (0 00-1). That's 2 cranks instead of 27 necessary to wind in 999.

[@marcel911]

So, the smaller digits on the keys are just the 9's complement. So subtraction is 9's compliment addition.

[@BokBarber]

Technically 10s compliment because you add one, but yes.

[@bonniemoerdyk9809]

I used a comptometer in Business Machines Class back in 1970-71 in high school. I really don't recall doing anything besides addition, and I don't remember the little silver tabs. Maybe there were simpler models....or my memory is failing me....LOL

[@jaapsch2]

If your machine did not have the subtraction tabs, then you were probably working on a Burroughs calculator. www.jaapsch.net/mechcalc/burroughs.htm#videocalculators

[@canaDavid1]

for division - is there a binary (or any other base) equivalent? How would one generalize the algorithm?

[@radiorobertakaandy5982]

I've got one.it works,bit dont know how lol.

[@sustainfem]

Learned the comptometer in high school in the late '60s. To aggravate the (male) teacher (who we really liked and had a crush on), my friend and I entered so many numbers into the comptometer that it ran for a few minutes and the whole class stopped. He took it well, actually. I imagine someone probably did that every semester, lol.

[@qwertypoiuyeet4800]

Sorry. My wife was a comp. teacher. She says your technique could be improved

[@icanspotnything5brand751]

Haven"t got a clue what he's on about...

[@IanRM]

Me neither lol

[@andrewprince503]

Sorry but you arent explaining it well at all mate