NPR's Scott Simon talks to math historian Glen Van Brummelen about his finding that the decimal point appeared in the 1440s, earlier than thought.

The humble decimal point may have been invented about 150 years before we previously thought. Experts had previously credited German mathematician Christopher Clavius for the innovation, but ...

SIMON: He traced the decimal point back 150 years further than previously thought, to a little-known mathematician in Ferrara, Italy, named Giovanni Bianchini.