Short answers, pulled from the story.
Ancient Egyptian hieroglyphs used a purely decimal system to record quantities around 3000 BCE. This early system relied on powers of ten without positional notation.
Archimedes invented a decimal positional system in his Sand Reckoner between 287 BCE and 212 BCE. His early work was based on 10 raised to the power of eight.
Simon Stevin published De Thiende in Dutch in 1585 introducing a forerunner of modern European decimal notation. This publication established key principles for decimal fractions in Europe.
Any real number that is not a decimal fraction possesses a unique infinite decimal expansion. Long division allows computing this infinite expansion which repeats the same sequence of digits indefinitely if the number is rational.
Early computers such as ENIAC and IBM 650 utilized decimal representation for internal operations. Modern database implementations often store values using variants of binary-coded decimal or decimal floating point standards instead.