Note the fractions:
The denominators are powers of 10.
|They call themselves decimal fractions all fractions that have powers of 10 in the denominator.|
The French Viète (1540 - 1603) developed a method for writing decimal fractions. Instead of fractions, Viète would write comma numbers. This modernized method is still used today.
Note in the table the representation of decimal fractions by decimal numbers.
The numbers 0.1, 0.01, 0.001 and 1.17, for example, are decimal numbers. In this representation, we find that the comma separates the whole part from the decimal part.