The 1750 Act reforming the legal year also officially introduced to England the Gregorian calendar on Thursday 14 September 1752. Up until then, England had been using the Julian calendar, which by that time was eleven days behind the calendar of most countries on the European Continent. So events before 1752 in English records often differ from European records, and it is sometimes necessary to refer to both sets of dates using "Old Style" (Julian) and "New Style" (Gregorian) notation, e.g. William of Orange's armada landed in England on 5 November 1688 (OS) or 15 November 1688 (NS)(see Old Style and New Style dates).