Quaker records before 1752 used the Julian calendar AND did not use the names of the days of the week as they were based on Pagan gods. This has caused a lot of confusion in the way the dates are reported; some secondary sources report the dates wrongly, so it's best to view a primary source to avoid compounding errors. In a nutshell, "first day" is Sunday, and "first month" is March. The months were written as lower case roman numerals. You may also see this abbreviation "o.s." (old style) next to a date. For more detailed information here's a site with a good description of the calendar change and the problems that may be encountered: Quaker Dates
Another good source on the calendar change is ancestry.com. They can explain this much better than I can. The English and their colonies base their dates on the Julian calendar, whereas after 1752, the Gregorian calendar was the "new" calendar. There was a very confused period from Dec. 31, 1751, as this was followed by Jan. 1, 1752 when the calendar changed. Not only that but the rest of Europe as well as Scotland adopted the Gregorian calendar before 1752. Aieee.
Use of Double-dating
No, not when you go out with your sister's friend, your sister and her date!
Direct quote: "Double dating was used in Great Britain, colonial British America, and British possessions to clarify dates occurring between 1 January and 24 March on years between 1582 and 1752. In the ecclesiastical or legal calendar, March 25th was recognized as the first day of the year and was not double dated. Researchers of colonial American ancestors will often see double dating in older records. Double dates were identified with a slash mark (/) representing the Old and New Style calendars, e.g., 1690/1691. Even before 1752 in colonial America, some educated clerks knew of the calendar change in Europe and used double dating to distinguish between the calendars. This was especially true in civil records, but less so in church registers. Researchers will often see this type of double dating in New England town records, court records, church records, and wills, or on colonial gravestones or cemetery transcriptions. The system of double dating ended in 1752 in the American colonies with the adoption of the Gregorian calendar". source ancestry.com magazine archive 11/1/2000 issue.