Determination of the day of the week not a Gregorian leap year, (but 19 in the Julian column indicates that it "is" a Julian leap year, as are all Julian "x"00 years). 20 indicates that 2000 is a leap year. Use Jan and Feb only in leap years. For determination of the day of the week (1 January 2000, Saturday) For determination of the dominical letter (2000, BA) For determination of the doomsday (2000, Tuesday) Note that the date (and hence the day of the week) in the Revised Julian and Gregorian calendars is the same from 14 October 1923 to 28 February AD 2800 inclusive and
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