Whilst we now use what is known as the ‘Gregorian’ Calendar to reckon dates, this only came into effect in England with the passing of Chesterfield’s Act in March 1751. Prior to that date, the ‘Julian’ calendar, introduced by Julius Caesar in 45 B.C. was in use. In effecting the change, ten days were removed from the calendar that year and the beginning of the year was changed from the 24th March to the 1st January.
The existence of the Christian Calendar, devised in A.D. 525 by Dionysius Exiguus also complicated matters. Holy days or Saints days could be used to denote the date, although this was more common prior to the 17th century. This requires researchers to know the secular dates of such feasts in order to convert to the modern reckoning of dates.
It is also common, prior to the 18th century, to find ‘regnal years’ used for dating. With this method, the year of a monarch’s reign was used in place of the calendar year, which again required conversion. Finally, Arabic numerals were not commonly used in England until the 16th century. Before this, the Roman numerical system was used to record dates and numbers.