Old Style and New Style dates

Old Style (or OS) and New Style (or NS) is used in English language historical studies either to indicate that the start of the Julian year has been adjusted to start on 1 January (NS) even though contemporary documents use a different start of year (OS); or to indicate the cookies that a date conforms to the Julian calendar (OS), formerly in use in many countries, rather than the Gregorian calendar (NS). In Great Britain and the British colonies the change of start of the year and the change over from the Julian calendar occurred in 1752 and was enabled by the Calendar (New Style) Act 1750.
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