Decimal numbers are non-integer numbers in which the decimal part is separated with a comma. Their use was found in an ancient manuscript dating back to 1440 circa by Giovanni Bianchini, a Venetian merchant.
Bianchini is therefore a century and a half ahead of the first known use of the decimal point, which until now was attributed to Cristoforo Clavio. The discovery suggests, therefore, that Bianchini played a more important role in the development of the foundations of mathematics than he believed.