Originally (near the end of the 1st millenniumCE), a bar over the unitsdigit was used. Later, a separator (a short, roughly vertical, ink-stroke) between the units and tenths position became the norm. When type-set, it was convenient to use the existing comma, stop, or point marks for this purpose.
In many countries, therefore, the comma is used to mark the decimal units position; however, in predominantly English-speaking countries, a stop (.) or point (middle dot: ·) is commonly used as the decimal separator.
In Switzerland(mainly German-speaking Switzerland): 1'234'567,89
In the United Kingdom and United States: 1,234,567.89 or 1,234,567·89; the latter is more commonly found in older, and especially handwritten, documents nowadays; many UK schools now teach the SI style.
SI style: 1 234 567.89 (dot countries) or 1 234 567,89 (comma countries)
Countries where a dot is used to mark the radix point include: