No, this is not a guide to finding a significant other. Sorry.
Putting things into chronological order has been a challenge ever since someone tried to do it. Now is easy, yesterday, last spring, not too bad. But what about events prior to when your parents were alive? And how do you determine the start date? That’s where things get tricky: YBP, KYA, MYA, AH, YSC, AUC, BCE/CE, BC/AD, ACR . . . What a mess!
Where do you begin? The creation of the world? Which world? The Mayan long count began with the start of the 5th world (the one currently in operation). The start of the current dynasty? The reign of some long-ago ruler? The founding of the country or the re-founding (like the fictional Azdhagi re-starting their dating system with the Great Relocation, so all dates are BGR or AGR.)
The Chinese used the year of the emperor’s reign, so you might have Wen 24 (a Han Dynasty ruler) as the year, then the month and day.
The Jewish year system starts with creation, so the current year is 5776. There is no “before creation” notation because what came before the creation of the world? Chaos. [No, it was not an election year.] There was a brief flirtation with something similar when Bishop Ussher devised his date for creation (using BC) but no one wanted to shift the standard used in Western Europe and the current and former British colonies. There’s also the challenge of geologic dating if you are a scriptural literalist. I’ve also seen a few dates given as “since the Fall of Jerusalem” but that seemed to be an idiosyncrasy of the author more than a convention for dates.
Western Christianity used the Roman system at first, then shifted to Anno Domini “the Year of our Lord” and added Before Christ once Biblical Archaeology became “a thing” in the 1700s-1800s. Rome used the names of the two consuls at first (it was in the year that X and Y were consuls that . . .) and later used the founding of Rome as the start point for their calendar. Marcus Terentius Varro fixed that at (Western usage) 753 BC. Romans used AUC – ab urbe condita, “after the founding of the city” and this year is 2769 auc.
The Russian Orthodox Church has changed calendars a few times. Until 1918 Russia used the Julian calendar, which is why the October Revolution took place in November, Western Style. Before the late 1400s the new year began on Sept 1, then shifted during the reign of Peter the Great. I have a book that seems to show dates from the conversion of Rus, so 998 is the starting year, but I’m not quite certain what else is involved. It is a book for people who already know how Muscovy “worked” and the author doesn’t give any clues as to the rest of the calendar, sine he is quoting legal documents from Muscovy. Most of the dates he gives are the conventional western calendar years.
Islam dates everything from the Hejira, Mohammad’s flight from Mecca to Medina, and their dates are AH. If you try to line Islamic calendar years up with western years it won’t work, because the Islamic calendar is a free-floating lunar calendar instead of a solar calendar, or a fixed lunar calendar (Jewish calendar). This is currently 1430 AH. If you want to date things earlier you start running into difficulty for Islamic theological reasons as well as the lunar calendar complications, and most scholars shift to KYA or BP [see below].
The west got along pretty well with BC/AD, although non-Christians had some complaints. One compromise was to change AD to CE, which is either ‘Christian Era” or “Common Era” and then “BCE” Before the Common Era.
Archaeologists, anthropologists, and geologists developed a few other short hands that eliminated the whole “when does it start” problem. You get KYA, thousands of years ago, and MYA, millions of years ago. Plus you do not have to write out all those zeros, and if you are dealing with vague dates to begin with, it works well.
Carbon dating and then Kr/Ar and other isotope systems now use YBP, or “years before present” with 1950 being used as present. Everything that you need to date is from a long time ago, so it is YBP. You don’t have to mess with negative numbers as often, no one can be offended because it uses the date of the birth of someone they don’t believe existed or who wasn’t that important, and its strictly arbitrary so it does not favor one culture.