How Did Jewish Women Know When To Light Shabbat Candles in the 18th C.?

With a hat tip to Mississippi Fred MacDowell, I'd like to point your attention to Lion of Zion's article of
How Did Jewish Women Know When To Light Shabbat Candles in the 18th C.?

Keep this article in mind when deciding whether to hold 18 or 20 minutes before sundown for candlelighting