It can be considered to be based on the conversion between Julian day and the calendar date .
Zeller 's congruence is an algorithm devised by Christian Zeller to calculate the day of the week for any Julian or Gregorian calendar date .
congruence can be considered to be based on the conversion between Julian day and the calendar date .
Zeller 's congruence is an algorithm devised by Christian Zeller to calculate the day of the week for any Julian or Gregorian calendar date .