How the date of the Revel celebrations is decided

From an article written by the Revd Samuel Holker Haslam. Vicar of Week St. Mary 1900-1919.

The Revel: The question has been asked why we keep the Revel or Dedication Festival on the first Sunday after September 15th. The following facts partly or wholly explain the matter... Our church is dedicated to Blessed Virgin Mary, whose nativitiy is commemorated on 8th September. In connection with these Church Festivals grew the Village Fair Day, Pay Day and so on. Thus, it is recorded in the old registers of this parish, that a Fair was held at Week St. Mary on September 8th, and certain items appear in the Churchwardens' Accounts as having been paid on the Fair Day. Now it happens that in 1762 by Act of Parliament eleven days, namely September 3rd to 18th inclusive were struck out of the Calendar, and if any Fair were held or any notice taken of the Nativity in that year, it could not possibly have been on the 8th for that was one of the days struck out. In that year September 1st would be Tuesday, September 2nd Wednesday, the next day Thursday had to be called 14th and Friday the 15th, and so on. The calendar had got nearly 12 days behind time.  What people were calling September 3rd was really September 15th. Having then got between a week and a fortnight wrong "in numbering our days" what was to be done?  It was probably best, as far as the Fair and money was concerned, as people had got without knowing it between a week and a fortnight behind time, to keep so; any further getting behind time in future would be prevented by cutting out the 29th February every fourth year, except the centuries; but it should still be understood that in the Calendar the 8th is still the Nativity of the Blessed Virgin Mary and that was the original Festival and Fair of the Parish of Week St. Mary.