Home Marchant 8ADX Mechanical Calculator Repair and Operation.

Marchant 8ADX Mechanical Calculator Repair and Operation.


Marchant 8ADX

Left Side


In the 1940s, Marchant opted to redesign the casing and outer design of their Silent Speed models. Joseph Sinel was hired and created a sleek, smooth, elegant design that debuted in the 1950s. This casing consisted of multiple pieces that interlocked and had to be assembled into a specific order. This resulted in the Figuremaster, a machine with a clean curved case with no screws to be seen.


Inside, the machine remains largely the same, with only minor changes. Changes such as the carriage shift keys being moved from the far right to above the clearing mechanism. This model, the 8ADX also had the carriage tabulators and division setup button, and was built in 1956. This machine came from Muncie, Indiana and even had the original cover, felt pad, and a removable + branded decimal marker.



The carriage consist of a 8 digit counter register at the top right. Below that is the carriage tabulator keys. At the bottom is a 16 digit accumulator register. Below each register are decimal indicators that can be rotated manually 90 degrees to reveal a white dot indicating a decimal place.



The keyboard consists of 8 columns of keys numbered 1-9. Above the keyboard is a digit entry register that allows for checking if the correct digits have been pressed on the keyboard. Above the register is a sliding piece with an orange point that allows for some decimal visualization. There are no individual decimal markers on the keyboard for each column.

Control Keys

At the top left of the control keys is the DIVIDEND key. This key shifts the carriage all the way to the right and then adds the keyboard input into the accumulator for division. To the right of that key is the ÷ key. This key begins automatic division once it has been setup. Next is the STOP key. This key stops a multiplication or division process if pressed twice. To the right of that key, is a missing lever. Unfortunantly, the lever broke in shipping and I haven’t glued it back together yet. The lever function is to reverse the counter register.

Below the DIVIDEND key is the - and + key. These keys are simply used for addition and subtraction respectively. To the right of those keys is a NON SHIFT key. This key, when pressed, prevents the carriage from shifting to the left during multiplication. The STOP key can be pressed once to release the button. Below that key is the NEG X key. IF this key is pressed, when a multiplication is performed, the result of the multiplication will be subtracted from the accumulator instead of added to it.

Below that, are two carriage shift keys. And then below that, on the left is the KEYBOARD DIAL key that clears the keyboard. To the right, is the MIDDLE DIAL, UPPER DIAL, and CLEAR RETURN keys. The MIDDLE DIAL and UPPER DIAL keys clear the middle and upper registers. The CLEAR RETURN key clears the counter register and returns the carriage to it’s leftmost position.

And finally, on the very right of the control panel is the multiplication column.


Operating this machine is nearly identical to the Marchant “Silent Speed” ACR8M that I have already written about. However, division is slightly different with an added convenience. If you don’t know how division previously worked on the Marchant Silent Speed line, you can read about it here.


This machine has a button for automatically setting up division. On the ACR8M, the accumulator register had to be cleared, the carriage shifted to the left, and the the dividend had to be entered all manually. This is reduced to a single button press on the 8ADX. To setup division, simply enter the number onto the keyboard, and press the DIVIDEND key. The machine will clear, shift the carriage, and enter the dividend into the accumulator in one go. Then the divisor can be entered and the ÷ key pressed.


This machine just needed oiling and the counter reverse switch to be repaired. This machine had been kept in beautiful shape.


This machine still has its original cover! It has the SCM logo and Marchant name on it.


It is also came with the original felt pad the machine would have rested on, with the machines foot imprints left on it.

Felt Pad

And finally, it also came with a removable decimal marker I had never seen before. It has holes for keys, and rests on the keyboard, with a white line to indicate a decimal.

Decimal Marker

Decimal Marker

Cover Removal

Cover removal can be a bit tough thanks to the lack of visible screws and clever design of the elegant panels. First, the screws must be taken out of the bottom of the machine.

Cover removal 1

Then, set the machine down on it’s feet. The very back panel should pulled back, it’s hinged at the bottom.

Cover removal 2

Cover removal 3

The machine can now be lifted off of the bottom plate and back cover.

Cover removal 4

Next the front most panel needs to be removed. It is held in place by the keyboard panel and the baseplate. With the baseplate now gone, it can be removed easily. Next is the keyboard panel. This panel is the trickiest. It has three screws that need to be loosened, and two rods that need to be pulled to release it.

Cover removal 5

Black arrows indicate screw to be loosened, not removed. Red arrows indicate the rods to be pulled toward the front of the machine. With the three screws loosened, pull up on the front of the plate. Then use your other hand to pull each rod downward to release the back of the panel. Now with the keyboard cover off, the side panels can be freely removed.

Cover removal 6

The side panels simply have pins that rest in a rubber ring, two in the rear and one in the front of the machine. Gently pulling and wiggling the panel should be enough to free it.

Cover removal 7

And finally, the carriage cover can be removed via four screws, two on each side under the carriage. Now all the covers are removed for maintenance and oiling.

Machine Internals

Internals 1

Internals 2

Internals 3

Internals 4

Internals 5

Internals 6

Internals 7

Internals 8


This machine is very similar to the ACR8M. The ACR8M is still slightly faster, as the ACR8M has a slightly faster RPM motor. The internals are largely the same. No drastic new features are added with the ADX with the exception of the DIVIDEND key, which does make division simpler and quicker to setup. The ACR8M however, had keys for changing the direction of the carriage during multiplication, and a lever for clearing and returning after division. The keyboard has a slightly different layout, but no drastic changes. The machine even appears to be built with identical frame pieces:


The position of the carriage shift buttons changed between the two machines, however, twenty years later, the rightmost frame piece still has screw holes and pins for the shifting levers to be mounted there.

The machines do differ largely in appearance, but not in size.

Size 1

Size 2


Logo 1

Logo 2

Logo 3

This post is licensed under CC BY 4.0 by the author.