Mathematical historian explains why the origin of decimal point was way earlier than we think

Many a time we wonder how ancient people learned mathematics, science, geography or astronomy so perfectly without the resources that we have now. They were the pioneers of new civilizations that consistently evolved to bring about the modern technological world that we live in now. On that note, a recent finding showed that what we perceive to be the origin of "decimal numbers," is actually not accurate. A mathematical historian, Glen Van Brummelen, revealed its true origin in the study, "Decimal fractional numeration and the decimal point in 15th-century Italy," published by the Historia Mathematica.

As per Brummelen's findings, the first-ever usage of a decimal point was identified from historical records dating back to the 1440s. The earliest ever decimal point known to man so far was from 1593 - the interpolation column of a sine table in Christopher Clavius's Astrolabium. But over a century earlier, in Renaissance Italy, a Venetian merchant Giovanni Bianchini used decimal points in his Tabulae primi mobilis in his works of spherical astronomy and metrology. This decimal points system was used by Bianchini to determine the coordinates of planets. Until Bianchini's works caught Brummelen's attention, the 16th century Clavius was attributed as the first person to use decimals in history. 

During a math camp for middle schoolers, Brummelen and his colleague bumped into decimal numbers while translating a Latin manuscript by Bianchini who was also an astronomer. "I saw the dots inside of a table - in a numerical table. And when he explained his calculations, it became clear that what he was doing was exactly the same thing as we do with the decimal point," the mathematician explained in an NPR episode. "He was using the decimal point, actually, in two different contexts. We don't exactly know which was first, but probably he was using it in conjunction with surveying instruments to find distances across fields or altitudes of buildings and so on," Brummelen added.

What baffled the mathematician was how Bianchini, who worked as a court administrator for the Duchy of Ferrara, used the decimal system for astrological predictions. "What we read in the newspapers today is what's known as sun horoscopes. And they're very, very simplified compared to the practice of astrology back in the 15th century. The mathematics that's required means you need to be able to know exactly where the planets are at any given time. This is a very complicated mathematical problem," Brummelen explained. He believed that Bianchini's decimal system would've come in handy for the astrological necessities at the court of Ferrera. 

Brummelen's study states that Bianchini's decimal system was later borrowed by the renowned mathematician and astrologer from the 15th century, Regiomontanus. "He learned from Bianchini, adopted a number of the latter's innovations, and in some ways extended paradigms that Bianchini had established," the study infers. So, over a century later, when Clavius was working on his Astrolabium, a crucial concept of spherical astronomy, Bianchini and Regiomontanus's work would've already been familiar to him. "In the context of introducing 'geometric algebra,' to Euclid's Elements, Clavius cited Regiomontanus's trigonometry as an authority. He recognized the usefulness of decimal fractional notation in the context of interpolation within a numerical table, but it was not his idea," the study concluded.