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The Centigraph Adding Machine: A Groundbreaking Invention in the History of Computing


In the annals of computing history, the late 19th century often gets overshadowed by the rapid advances of the 20th century that led us from vacuum tubes and punch cards to microchips and touchscreens. But this era saw an explosion of innovation in mechanical calculation that laid the foundation for the digital revolution to come. One of the most ingenious and influential devices to emerge from this period was the Centigraph adding machine, patented by Arthur E. Shattuck in 1891.

As a digital technology expert, I‘ve always been fascinated by the clever design principles and engineering challenges behind early computing devices. The Centigraph is a prime example of how inventors like Shattuck were able to create remarkably efficient and reliable calculating machines using nothing but gears, levers, and springs. In this article, we‘ll take a deep dive into what made the Centigraph so special and explore its lasting impact on the development of office automation technology over the past century.

A Mechanical Marvel: How the Centigraph Worked

At the heart of the Centigraph‘s adding mechanism was a pair of discs or wheels – one with 100 notches around its circumference and the other with 20 notches. Five numbered keys on the top of the machine controlled pawls that engaged with these notched wheels to input numbers up to 99. Pressing a key would rotate the 100-notch wheel a corresponding number of positions, displaying the result in a small window. The 20-notch wheel acted as a carry mechanism, allowing the machine to handle sums greater than 100.

Centigraph Adding Machine Diagram
Diagram of the Centigraph‘s key mechanism from Shattuck‘s 1891 patent

What set the Centigraph apart was its elegant handling of carries using a spiral groove and pin system. As the 100-notch wheel completed a full rotation, the pin would follow the groove and smoothly increment the hundreds place on a separate dial. This allowed the machine to calculate sums up to 599 – a significant leap forward from earlier single-digit adders.

To reset the machine after a calculation, the user simply turned a knob to release the carry mechanism and spun the wheels back to zero. Shattuck‘s design was a model of mechanical efficiency, requiring just a single full 360° turn to clear even the largest sums.

How the Centigraph Stacked Up

Compared to other adding machines of the late 19th century, the Centigraph stood out for its simplicity and reliability. Let‘s see how it compares to two of its most notable contemporaries:

Device Inventor Year Max Sum Mechanism Keys
Centigraph A. Shattuck 1891 599 Gears, springs, carry disc 5
Comptometer D. Felt 1887 9,999,999 Gears, levers, carry mechanism 8 per column
Grant rotary G. Grant 1877 999 Gears, cylinders 18

While the Comptometer and Grant rotary could handle larger sums and had more flexibility with multiple input columns, the Centigraph was much simpler and cheaper to manufacture. Its five-key input system made it very quick to operate for basic addition tasks. As we‘ll see, this focus on practical usability and affordability was key to the Centigraph‘s success.

Manufacturing and Selling the Centigraph

Getting a complex mechanical device like the Centigraph from the drawing board to the production line was no small feat in the 1890s. Shattuck faced numerous challenges in sourcing materials, fabricating precision parts, and assembling his adding machines at scale.

Based on surviving production records and advertisements, it‘s estimated that the Centigraph Company and later the American Adding Machine Company produced somewhere between 3,000-5,000 total units over the device‘s 10-15 year commercial lifespan. At the height of production in the mid-1890s, the companies were likely assembling several hundred Centigraphs per year.

One factor that helped boost production was Shattuck‘s decision to partner with experienced machinists and manufacturers. His 1887 patent was co-authored by Brainard Smith, a toolmaker who likely assisted with prototyping and refining the design for mass production. Later, the American Adding Machine Company had the resources and infrastructure to scale up manufacturing after acquiring the rights around 1902.

To sell the Centigraph, Shattuck and his partners leveraged the growing trade press and exposure at industry events. Advertisements and favorable reviews appeared in publications like The Office, The Bookkeeper, and The Phonetic Journal in the early 1890s. Centigraphs were often sold alongside or even bundled with early typewriters as a complete "modern office" package.

At a price point of $10-25 ($300-800 adjusted for inflation), the Centigraph was relatively affordable for small businesses looking to automate routine calculations. It was particularly popular with banks, insurance firms, and retail stores. In many cases, a single Centigraph could handle the workload of 2-3 human clerks, providing a rapid return on investment.

Impact on the American Office and Workforce

The Centigraph‘s greatest legacy is arguably its role in ushering in an era of office automation that transformed the American workplace in the late 19th and early 20th centuries. Along with the typewriter, carbon paper, and other innovations, adding machines like the Centigraph began to reshape how companies processed and utilized business information.

One major shift was in the gender makeup and job roles of clerical workers. Traditionally male professions like bookkeepers, accountants, and clerks increasingly became the domain of women office workers in the early 1900s. Automated tools like the Centigraph made many routine calculations and record-keeping tasks less dependent on specialized math skills, paving the way for a feminization of office labor.

As office scholar Sharon Hartman Strom notes in Beyond the Typewriter: "In 1890 no fewer than 75 clerical occupations existed, of which women represented only 9.4%, but in 1930 there were only about 45 clerical occupations left, of which women accounted for 51.5%."

Adding machines also changed the relationship between workers and information. Clerks could process data and generate reports far faster than before, giving managers unprecedented real-time visibility into sales, expenses, and other key business metrics. This shift towards data-driven decision making and analytics was a key enabler for the rise of modern corporate management practices.

The Arc of Mechanical Calculation

To fully appreciate the Centigraph‘s place in computing history, let‘s zoom out and look at the long arc of innovation in mechanical calculation:

  • 3000 BCE: The first abacuses are developed in Mesopotamia, using beads to represent numbers
  • 1600s: Early mechanical calculators like the Pascaline and Leibniz wheel are invented but not widely adopted
  • 1820s: Charles Babbage designs his Difference Engine, the first automatic calculator (never fully built)
  • 1870s: First commercially successful adding machines like the Grant rotary and Burkhardt arithmometer appear
  • 1887: Dorr Felt patents the Comptometer, the first multi-column adding machine
  • 1890s: The Centigraph and other simpler adding machines gain widespread adoption in American offices
  • 1900s-1960s: Mechanical and electro-mechanical calculators dominate, including classics like the Marchant and Friden
  • 1970s: Electronic calculators begin to displace mechanical models, dropping to affordable pocket sizes by the end of the decade
  • 1980s-present: Calculators are largely subsumed by the rise of PCs and mobile computers, living on as mobile apps and web tools

Throughout this long evolution, we see a consistent drive towards faster, more flexible, and more accessible number crunching. In its time, the Centigraph represented a key milestone in making mechanical calculation practical and affordable enough for mass adoption in the business world.

But it‘s fascinating to consider alternate histories where mechanical calculation evolved differently. What if Babbage had completed his Analytical Engine in the 1800s, jumpstarting the development of programmable computers? What if the Centigraph had been more fully developed to handle subtraction, multiplication, and division?

While we‘ll never know for sure, studying devices like the Centigraph offers tantalizing glimpses into the roads not taken in computing history. At the same time, they remind us of the enduring human ingenuity and creativity that has driven technological progress for centuries.


From ancient abacuses to modern digital computers, the story of calculation technology is in many ways the story of human civilization itself. Our ability to process and analyze increasing amounts of numerical information has been a key driver of social, economic, and scientific advancement.

Devices like Arthur Shattuck‘s Centigraph played a pivotal role in this story by bringing mechanical calculation within reach of the average office worker and small business owner. While it may seem quaint by modern standards, the Centigraph was a mechanical marvel that exemplified the best of American engineering and entrepreneurship in the late 19th century.

As we continue to push the boundaries of digital computing power today with artificial intelligence, quantum computing, and other cutting-edge technologies, it‘s worth reflecting on how far we‘ve come from the days of wheels, pins, and springs. But in many ways, the spirit of innovation and problem-solving that drove pioneers like Shattuck lives on in the work of today‘s computer scientists and technologists.

So let us celebrate the unsung heroes of computing history like the Centigraph and its clever creator. May their stories continue to inspire us to use technology in the service of human flourishing for generations to come.