Russian data

[PYMCCART at ECUVAX.CIS.ECU.EDU]

The Eastern Orthodox Churches are evidently individuated by
states/nations, being most prominent in eastern Europe
and Russia.  The autonomy of statehood seems reflected also
in some of the practices of state churches, the calendar
being a rather divisive issue among them.
 
A schism between Old and New Calendarists developed in this
century, when in 1923 several state churches approximated the
Gregorian Reform of 1582.  The Russian and Greek churches were
among those represented at an ecumenical council in which the
reform proposal was approved.
 
Technically, they did not fall into step with the Greogrian
calendar, even though they skipped the requisite number of
days to agree with it.  They additionally adopted the new
leap-year rule Chris Carrier has mentioned: Leap year every
four years except years which leave remainders of 200 or 600
when divided by 900.
 
(http://ecuvax.cis.ecu.edu/~pymccart/orthodox-reform.html)
 
Not all state churches agreed to the reform, and some churches
split internally over it.  I have read that a subsequent
compromise has been attempted, whereby the New Calendarists
have readopted the Julian calendar for fixing moveable feasts
related to Easter (the principal issue of contention), but
observe other feasts, like Christmas, in agreement with the
Gregorian calendar.
 
As for the Orthodox church of Finnland, I have seen it mentioned
in a few places as a lone exception, having adopted the
Gregorian dates for all feasts.  The explanation given is usually
that the Christian population of Finnland is overwhelmingly
Western in orientation, so the Orthodox in Finnland prefer to
fit in.
 
As for the FORMULA for computing Orthodox Easter, it would
be the same as the Western formula, since both Churches regard
the Council of Nicaea in 325 AD as authoritative.  But because
of the differences in the Julian and Gregorian calendars, the
date of the Vernal Equinox (March 21) differs by about two weeks.
There's another difference, too: relating to when/WHERE the
moon is full.
 
(http://cssa.stanford.ecu/~marcos/ortheast.html)
 
--Rick McCarty