Analysis of information sources in references of the Wikipedia article "小数" in Japanese language version.
10.5.3 Grouping digits
Because the comma is widely used as the decimal marker outside the United States, it should not be used to separate digits into groups of three. Instead, digits should be separated into groups of three, counting from the decimal marker towards the left and right, by the use of a thin, fixed space. However, this practice is not usually followed for numbers having only four digits on either side of the decimal marker except when uniformity in a table is desired.
10.5.3 Grouping digits
Note: The practice of using a space to group digits is not usually followed in certain specialized applications, such as engineering drawings and financial statements.
