also: さ
numeric
one hundred-millionth; 10⁻⁸
Obsolete numeric unit representing 10⁻⁸, used in historical or classical Japanese numbering systems. Not used in modern everyday counting.
古典の数学書では、沙は一億分の一を表す単位として出てくることがある。
In classical mathematical texts, 沙 sometimes appears as a unit representing one hundred-millionth.
The historical derivation is uncertain; the kanji 沙 is used here as a specialized numeric character for 10⁻⁸ in traditional Japanese numbering.