Brunsviga Model D13ZK

Serial Number: 223277

Date: ca. 1947

Capacity: 10x8x13 + 10x8x13  (But only the right-hand bank has a revolutions counter)

Price paid: £75

This is an interesting machine, not least because it was the first machine that I  restored cosmetically beyond the usual cleaning and polishing.  I also regard this as a machine that has narrowly avoided being lost to history.

Machines of this type were used for co-ordinate transformations, gunnery calculations, and complex number calculations.  Since obtaining this machine, I managed to locate this Artillery Manual from 1944.  It is noted that the worked examples in the manual (in Chapter 2 specifically reference the Twin Marchant machine then in use in the British Army; however, the examples can be modified to suit the Brunsviga.

The model number indicates (Z) that the revolutions counter has tens (zehn) carry and a combination (K) clearing option – in this case, the right hand lever clears only the revolutions counter, or the revolutions counter and the input registers, depending on the position of the switch on the right hand side of the front plate (position 1 for rev counter, position 2 for rev counter plus input registers).  The lever on the left clears the input registers, and the result registers (accumulators) are cleared independently via the lever to the right of each register.  There is no back transfer facility on this machine.

The switch in the centre of the front plate selects either (left) both rotors rotate in the same direction, or (right) they rotate in opposite directions.  In the central position, the left-hand machine is disconnected, and the right-hand machine operates as a normal 13ZK.

The revolutions counter is unusual (in common with other German made Brunsvigas) in that the number wheels are marked with two sets of numbers; white numbers to count positive revolutions, and their complements alongside marked in red to count negative revolutions. The appropriate set of numbers is automatically selected by a sliding masking plate, depending on the direction of the first turn of the crank.

When any of the registers are partially cleared, red indicators are visible next to the relevant register, and the machine is blocked.  A green indicator shows next to the revolutions counter when it is reset.

Numbers can be entered directly into either of the accumulators by depressing the lever on the front left of the appropriate register and rotating the rubber-tyred wheels below the register.  Or they would if the rubber on some of the wheels hadn’t perished.

Cosmetic Restoration

I have stated elsewhere on this site that I like machines to look used.  However, this can go too far!

The only mechanical restoration involved getting everything moving with WD40 and lubricating oil, while avoiding getting oil on the pinwheels themselves.  The most recalcitrant part was the sprung pin in the main crank which was rusted firmly in place – without moving this, the crank could not be turned at all.  Once this was freed, the machine was found to move quite well.  The carriage was also rusted in place.  Again, plenty of lubricating oil and not so gentle persuasion got it moving again.  Despite decades of neglect, internally the machine is actually in reasonable physical condition.

All of the panels were removed, and the paint removed (if possible) using paint stripper and wire wool. The front panels were made from aluminium, which proved easier to strip then the steel panels.  Where stripping was not possible, the panels were roughened with wire wool and resprayed.

Black acrylic car paint was used to spray everything, and, after allowing time for drying, the recessed numbers and other details were filled with acrylic paint, the excess being wiped off with a damp cloth while the paint was still wet.

The main crank handle and the resetting cranks were rubbed with wet or dry paper (wet, in this case) to remove the rust and peeling chrome plating, as were the strips holding the decimal markers.

While it’s not perfect, it’s a lot better than before.


Before Restoration


Brunsviga Model 13ZK

Serial No. 222005

Date: ca. 1947

Capacity: 10x8x13

Price paid: £30

This is essentially the machine of which two were used in the construction of the double Brunsviga shown above.  The only difference is that there are no wheels on the carriage register for the direct setting of dividends.

Brunsviga Model Nova II

Serial No. 118134

Date: Early 1930s

Capacity: 10x10x15

Price paid (including postage): £25.50

This machine came complete with its original steel cover and fitted base, and was described, if I recall correctly, as being in “poor condition”.  I’ve had far worse machines which have been described as being in good condition.  The covers have been repainted.

The machine has all of the usual Brunsviga refinements – tens carry and auto-reverse on the revolutions counter, and back transfer being among them.

In common with other Brunsviga machines, and the Busicom HL-21, the control register numbers rotate when the main crank is operated – unlike most other machines where they remain static.

To operate the back transfer mechanism:

1) Clear the input register using the upper lever on the left hand side;

2) Pull the lower lever fully forwards against spring pressure;

3) While holding the lever in the fully forward position, clear the accumulator in the normal way – while the accumulator is being cleared the contents will transfer to the input.

This is a heavy machine which has the effect of making it wonderfully smooth to operate, and less prone than lighter machines to wander across the desk.  Because the pinwheel rotor is heavy and the crank has a lot of leverage, the resistance encountered when underflow or overflow takes place is less noticeable than on smaller, lighter, machines.


Brunsviga Model 20

Serial No. 215398

Date: ca. 1947

Capacity: 12x11x20

Price paid:  This machine, along with the Triumphator KN and Sterling “Plus” Adder shown elsewhere on this site, was a very generous gift from Colin Jackson of Heptonstall, West Yorkshire.

This is a very heavy machine (12kg or 25 pounds) which was in production for 30 years from 1934.  Later machines were finished in the metallic bronze of the Model 13RK shown below, but until the 1950s all Brunsvigas were black (as far as I am aware).

This is a fully featured machine with all of the refinements of a top of the range machine.  Slightly unusual refinements include the ability to selectively clear the accumulator (either all or the right hand half only), and the provision of thumbwheels to enable numbers to be directly set into the accumulator.

Back transfer is effected by pulling the lever on the left towards you, clearing the input register.  If the lever is pulled further against a spring and held there, clearing the accumulator with the bottom lever on the right transfers its contents to the input register.


Brunsviga Model 13RK

Serial No. 13-63530

Capacity: 10x8x13

Date: 1950s

Price paid (including postage): £40 with the Facit CM2-16

This is a solidly constructed machine. with all of the usual Brunsviga refinements such as a control register, tens carry on the revolution counter, and a back transfer.  The switch on the right front of the machine selects the clearing mode.  In its upper position, the top lever on the right clears both the revolution counter and the input register, and the middle lever on the right clears everything.  In its lower position, the top lever clears only the revolution counter, and the middle lever clears the revolution counter and result register (accumulator).  All of the registers can be cleared individually with the switch in the lower position.

The back transfer operates in exactly the same way as the Brunsviga 20.


2 thoughts on “Brunsviga

  1. Re Model D13ZK. Sir, I am most interested in this machine -and even more so now that I have read your comments in your dissertation. I was a Class 1 Artillery Surveyor and used this model rather extensively in the early 60’s. I have also been searching for this model for many years – and for my pains I have acquired two Brunsviga machines, namely two 13 Z and one model 13 RK. Just to reacquaint myself with this model, am I correct in thinking that this is the model that converts Polar co-ordinates to cartesian (Easting & Northings). Obviously, I have forgotten most of that which I ever knew about the machine, but at 85 years of age, I am completely computer literate. Indeed, I have written three books since I turned 65 years of age.
    Do please contact me if this machine is available for sale. Ì am deeply interested.

    David Morris Moodie.

    Tele No. 01887 840329.


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