Context: "Old Style" (OS) and "New Style" (NS) are sometimes added to dates to identify which system is used in the British Empire and other countries that did not immediately change. Because the Calendar Act of 1750 altered the start of the year, and also aligned the British calendar with the Gregorian calendar, there is some confusion as to what these terms mean. They can 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 that a date conforms to the Julian calendar (OS), formerly in use in many countries, rather than the Gregorian calendar (NS).

Question: What designation was added to British dates to differentiate them from countries not using the new calendar? 
Answer: "Old Style" (OS) and "New Style"

Question: When was the Calendar act enacted?
Answer: 1750

Question: With what did the Calendar Act align the British calendar?
Answer: Gregorian calendar

Question: What did the use of Old Style and New Style cause?
Answer: confusion

Question: What law did the British make to cause the use of the Gregorian calendar?
Answer: Calendar Act of 1750

Question: Why are old-style new style not using the British Empire?
Answer: Unanswerable

Question: What did the calendar after 1752 to clarify the meaning of old-style new style?
Answer: Unanswerable

Question: What did the calendar act aligned with the British calendar?
Answer: Unanswerable

Question: What this OS indicate January 1 is?
Answer: Unanswerable