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Origins of our calendar

Approximately 1600 years later, the small difference had grown to a whole 10 days. Pope Gregory XIII decided to put an end to this imprecision by forming the papal bull

"inter gravissimas"

in the year 1582.

He excised 10 days from the calendar. The Franconian mathematician Clau, known as Clavius, who was appointed by him, founded the well known and still valid today regulation whereby the year has just 26 seconds too many. A day must only be omitted in the

Gregorian Calendar

every 3333 years.

Leap year rule DIN EN 28 601

A leap year is a year which is exactly divisible by four, unless it is a century year whereby the year must then be exactly divisible by four hundred.

The official translation of "Inter gravissimas pastoralis officii nostri curas" (start of the papal bull): "Among our serious pastoral duties, not the last is that we care, . . .",

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