# The Decimal Point Is 150 Years Older Than We Thought, Emerging in Renaissance Italy

HisÂ­toÂ­riÂ­ans have long thought that the decÂ­iÂ­mal point first came into use in 1593, when the GerÂ­man mathÂ­eÂ­matiÂ­cian ChristoÂ­pher ClavÂ­ius wrote an astronÂ­oÂ­my text called AstroÂ­labiÂ­um. It turns out, howÂ­evÂ­er, that the hisÂ­toÂ­ry of the decÂ­iÂ­mal point stretchÂ­es back anothÂ­er 150 yearsâ€“to the work of the VenetÂ­ian merÂ­chant GioÂ­vanÂ­ni BianÂ­chiÂ­ni. In his text TabÂ­uÂ­lae priÂ­mi mobilis, writÂ­ten durÂ­ing the 1440s, BianÂ­chiÂ­ni used the decÂ­iÂ­mal point to calÂ­cuÂ­late the coorÂ­diÂ­nates of planÂ­ets. In so doing, he inventÂ­ed a sysÂ­tem of decÂ­iÂ­mal fracÂ­tions, which, in turn, made the calÂ­cuÂ­laÂ­tions underÂ­pinÂ­ning modÂ­ern sciÂ­ence more effiÂ­cient and less comÂ­plex, notes SciÂ­enÂ­tifÂ­ic AmerÂ­iÂ­can.

Glen Van BrumÂ­meÂ­len, a hisÂ­toÂ­riÂ­an of mathÂ­eÂ­matÂ­ics, recentÂ­ly recountÂ­ed to NPR how he disÂ­covÂ­ered BianÂ­chiniâ€™s innoÂ­vaÂ­tion:

I was workÂ­ing on the manÂ­uÂ­script of this astronomer, GioÂ­vanÂ­ni BianÂ­chiÂ­ni. I saw the dots inside of a table â€” in a numerÂ­iÂ­cal table. And when he explained his calÂ­cuÂ­laÂ­tions, it became clear that what he was doing was exactÂ­ly the same thing as we do with the decÂ­iÂ­mal point. And Iâ€™m afraid I got rather excitÂ­ed at that point. I grabbed my comÂ­putÂ­er, ran up and down the dorm hallÂ­way lookÂ­ing for colÂ­leagues who still hadÂ­nâ€™t gone to bed, sayÂ­ing, this perÂ­sonÂ­â€™s workÂ­ing with the decÂ­iÂ­mal point in the 1440s. I think they probÂ­aÂ­bly thought I was crazy.

In a new artiÂ­cle appearÂ­ing in the jourÂ­nal HisÂ­toÂ­ria MathÂ­eÂ­matÂ­iÂ­ca, Van BrumÂ­meÂ­len explains the hisÂ­torÂ­iÂ­cal sigÂ­nifÂ­iÂ­cance of the decÂ­iÂ­mal point, and what this disÂ­covÂ­ery means for the hisÂ­torÂ­iÂ­cal develÂ­opÂ­ment of mathÂ­eÂ­matÂ­ics. You can read it online.

RelatÂ­ed ConÂ­tent

TrigonomÂ­eÂ­try DisÂ­covÂ­ered on a 3700-Year-Old Ancient BabyÂ­lonÂ­ian Tablet

How the Ancient Greeks Shaped ModÂ­ern MathÂ­eÂ­matÂ­ics: A Short, AniÂ­matÂ­ed IntroÂ­ducÂ­tion

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