Someone encountering an “Analytical Engine” today would probably think it was part of a mechanical system for some bizarre car—or perhaps an obscure telegraph machine or some kind of eccentric musical instrument. We probably would not recognize this jumble of pins and cogwheels as the world’s first computer. Although a working model was never completed, English mathematician Charles Babbage’s design, first described in 1837, was extraordinary. And it had parallels with the modern computer, such as its “mill”—what we would now call a central processing unit.

At the time there was one curious and imaginative mind that recognized the strange machine’s potential as a concept. In 1843 self-made mathematician Ada Lovelace published a paper that detailed how the Analytical Engine worked, and contemplated the kind of far-reaching tasks she imagined it could perform. She is, via her annotations on the calculating machine, widely thought to have made a large contribution to the field of computer science and now stands as an inspiring symbol for women scientists. In 2009 Suw Charman-Anderson, former executive director of the London-based nonprofit Open Rights Group, designated the second Tuesday in October (a date chosen arbitrarily) as Ada Lovelace Day to celebrate women’s achievements in math, science and engineering.

Lovelace lived a short but consequential life. Born in 1815 to a well-known aristocratic family, she was initially famous for being the daughter of English poet Lord Byron—who called Lovelace’s mother, Annabella Byron, the “Princess of Parallelograms” for her love for mathematics. Their marriage was short, and Lord Byron disappeared from both their lives when Lovelace was an infant. Annabella, terrified Ada might develop her father’s head-in-the-clouds romanticism, forbade her daughter from reading Lord Byron’s poetry, and instead surrounded the child with math.

It worked. She grew up with her head in a book, studying and questioning algebra and geometry, and showing a growing fascination with machinery. At 17 she and her mother attended an event where Lovelace first encountered Babbage. He was demonstrating the prototype for his “Difference Engine,” a simpler precursor to the Analytical Engine. The prototype was designed to calculate values based on a formula, reducing the manual labor required to create tables. The idea stoked Lovelace’s fascination with machinery, and she set out to understand everything about the Difference Engine. As she grew into adulthood, she had several mentors including mathematician Augustus De Morgan, who tutored her in 1840 and 1841 through an exchange of 63 letters. De Morgan was patient and kind, answering questions that had puzzled Lovelace, filling in the gaps in her mathematical knowledge. In a letter to Annabella he noted the young mathematician’s remarkable “power of thinking,” saying it was “utterly out of the common way for any beginner, man or woman.”

These exchanges provided material for a paper published in August 2017 in Historia Mathematica, presenting evidence for Lovelace’s mathematical prowess and countering some historians’ claims that her story may have been overhyped, and that she could not have had enough mathematical knowledge to have written the notes in her paper about the Analytical Engine—the feat for which she is best known.

In 1843 Ada translated a French paper written about Babbage’s machine—including her annotations, which were almost twice as long as the paper itself. These included a thorough description of the workings of the machine, including how paper punch cards could be used to adjust the machine’s settings. Lovelace also lingered on the possibility of using the device to compose music. And the notes went on to show how such a calculator might be able to compute a series of numbers that frequently pop up in higher arithmetic, called Bernoulli numbers—a process some might call the world’s first computer program. Her insights floored Babbage. In a letter to his friend and English scientist Michael Faraday he called her “that Enchantress who has thrown her magical spell around the most abstract of Sciences and has grasped it with a force which few masculine intellects (in our country at least) could have exerted over it.”

Adrian Rice, a mathematics professor at Randolph–Macon College in Virginia, and his colleagues at the University of Oxford spent long hours at the Bodleian Library in Oxford this past year, poring over and reordering the letters between Lovelace and De Morgan. They drew several conclusions about her mathematical strengths such as her tendency to make perceptive observations about concepts and her predictions about ideas that would turn out to be true. The researchers say that by the end of her correspondence with De Morgan she had reached a university-level understanding of mathematics, and that her teacher was already introducing her to open-ended abstract questions. “A lot of people base this opinion [that Ada’s accomplishments have been overblown] by saying that there’s no way she could have written this because she didn’t know enough math,” Rice says. “Well what we show in our papers [is] yes, she did have enough math—she could definitely have done it.” Rice adds he would consider her to be the world’s first “debugger” more than the world’s first computer programmer: For example, she found a large error that Babbage had made in his calculations, mirroring her attitude of questioning and finding mistakes in mathematical queries throughout her correspondence with De Morgan.

Lovelace died at just 36, but the science community has kept her legacy alive. In 1862, 10 years after her death, Scientific American published an excerpt from the Times of London that described an exhibition of machines, one of which was probably a half-built Analytical Engine. It read: “This is Mr. Babbage’s great calculating machine, which will work quadrations and calculate logarithms up to seven places of figures. It was the account of this invention written by the late Lady Lovelace—Lord Byron’s daughter—that led to Messrs. Scheutz, of Stockholm, to improve upon it to such an extent as not only enabled the machine to calculate its tables, but to print its results.”

Lovelace has gradually become a pioneering symbol for all women who are in or aspiring to join the crazy whirlwind of science. And the second Tuesday of every October becomes a recognition not only of her but of all the women throughout history whose contributions have been forgotten or overlooked—or never been found.