Determination of the day of the week day of the week begins by starting from an ‘anchor date’: a known pair (such as January 1, 1800 as a Wednesday), determining the number of days between the known day and the day that you are trying to determine, and using arithmetic modulo 7 to find a new numerical day of the week. One standard approach is to look up (or calculate, using a known rule) the value of the first day of the week of a given century, look up (or calculate, using a method of congruence) an adjustment for the month, calculate the number of leap years
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