Determination of the day of the week ISO 8601. The day designated with 7 may also be counted as "0", by applying the arithmetic modulo 7, which calculates the remainder of a number after division by 7. Thus, the number 7 is treated as 0, 8 as 1, 9 as 2, 18 as 4 and so on. If Sunday is counted as day 1, then 7 days later (i.e. day 8) is also a Sunday, and day 18 is the same as day 4, which is a Wednesday since this falls three days after Sunday. The basic approach of nearly all of the methods to calculate the
Names of the days of the week Sun and Moon ("sunnudagur" and "mánudagur" respectively), while dispensing with the names of the explicitly heathen gods in favour of a combination of numbered days and days whose names are linked to pious or domestic routine ("föstudagur", "Fasting Day" and "laugardagur", "Washing Day"). The "washing day" is also used in other North Germanic languages, but otherwise the names correspond to those of English. The ISO prescribes Monday as the first day of the week with ISO-8601 for software date formats. The Slavic, Baltic and Uralic languages (except Finnish and partially Estonian) adopted numbering but took Monday rather than Sunday as