The rhetorical device being used is <u>allusion</u>.
Explanation:
In November 19, 1863, the US President Abraham Lincoln delivered the Gettysburg Address to recognize and honor the effort of the fallen soldiers of the ongoing American Civil War and to encourage Americans to keep fighting. In the passage provided, which is also the opening of the speech, the President uses allusion because it briefly and indirectly refers to the day that the Declaration of Independence (1776) was issued when he says the phrase “four score and seven years ago,” which means “87 years ago” (score is equal to 20 years).
You would have to determine if the site is a credible soursce. Try to stay away from Wikipedia, not all information there is true. Also, make sure the information isn't outdated.
