Rheinmetall D IIa Calculator

This is a Rheinmetall calculator. Rheinmetall was an arms manufacturer, not unlike Walther, and it was founded in 1889 by Heinrich Ehrhardt in Düsseldorf. In around 1901 they acquired the pistols factory in Sömmerda, which is where the Dreyse pistols were made. And during the First World War they were the biggest or one of the biggest arms manufacturers for Germany. Of course, after the First World War they were not allowed to make arms any more and that is when the Sömmerda factory switched to making office machinery. They started with typewriters and in around 1921 or so they came out with the first calculator.

01:02 - It was designed by Richard Berk who had previously worked for Ludwig Spitz on the Unitas and TIM calculators. The interesting thing about this design is that the numbers are fairly close together, closer than you get with most stepped drum calculators like this, and this was done by having one stepped drum shared by adjacent digits. So when you have say 10 digits you only have five stepped drums. Around 1930, which is when this particular model was made, they started putting much more automation in the machines. They put in electric drive and also included automatic division.

02:05 - And this is one which allows automatic division. But other than that it’s a fully manual calculator. The basic functions are very straightforward. You can type in a number. The input that you’ve entered can be read back here on this input register. I have it on addition now - the A and the A here.

02:37 - The register and counter is clear, so if you now turn the crank, the input gets added to the register, the counter is incremented by one, and the keyboard is cleared automatically for the next input. Obviously any carries are performed automatically For multiplication you switch this lever downwards, and basically all that does is it ensures that the keyboard is not cleared after you’ve turned the crank. Let me just clear the register and the counter. So if i enter a number, now it’s not cleared so i can turn it a few times. I’ve turned it four times, so this is four times this input.

03:37 - To shift the carriage you can turn this knob here, and then multiply the number again for the next digit. So i have now multiplied this input number by 54. And this is the result. To clear the input you can use this button. Or you can clear a column individually using these red buttons at the bottom. And as i showed, the register is cleared with this, and the counter is cleared with this. To subtract, let me just first put in a big number. To subtract, you have to switch this left lever to subtract, and that’s how it works. It’s very straightforward really. The more interesting things are the automatic division Let me first shift the carriage to the right completely. Instead of turning this knob you can just slide it using this knob here. You have to lift it up first, and then you can slide it to the right.

05:09 - Note that the whole carriage doesn’t lift up like most older stepped drum machines, because on this one the gears are disengaged when it’s not in use, so that allows the carriage to slide freely without having to lift up from the mechanism. These knobs here allow you to enter any input you like. I’ll just input one. So there’s one in the register. I’ll put seven on the keyboard, and now I’m going to divide one by seven, so one seventh. I’ve put this lever down to subtract and division, and yes that’s all there is to it. Now I just have to turn the crank. On the first turn it subtracts, or tries to subtract, and it underflows, and I’ll keep turning.

06:24 - It doesn’t seem to do anything, but it’s now put in a different state where it is going to correct this previous subtraction. You can see that this C button has been pushed down. So it’s corrected it now by adding it again, and on the next turn it’ll automatically shift the carriage to the left, and now i can go for the next subtraction. Each time it subtracts So each time it subtracts until it underflows, it corrects that and shifts the carriage. There we go. So if I divide 1 by 7 I get 0.1428571. There’s a remainder of 3 here left. You may have noticed this C button here, which is interesting.

07:49 - Normally when you add or subtract the counter is incremented. But if you accidentally turn the crank once too often you can correct that by holding down the C button and turning it again. Then it subtracts and reduces the counter. If you were to fully subtract it would actually increase the counter. So holding down this C correction button it actually reverses fully the last turn of the crank.

08:38 - During the Second World War Rheinmetall again was manufacturing arms, and after the war the Sömmerda factory was in East Germany while the Düsseldorf and Berlin factories were in West Germany. The Sömmerda factory returned to making office machinery, and those were exported to the West through Berlin. And eventually they turned to making electronics and so on. The Rheinmetall company in the West, they eventually turned back to making arms and they are now a large arms manufacturer. So this was the Rheinmetall calculator. Thank you for watching! .