Change drawing scale to match a dimensioned line in Illustrator

This is a basic question that I hate to ask because it's really simple and I once knew the answer. How do I tell Illustrator the length of an existing line in a drawing that I've inherited? The particular line is supposed to be 690 mm long, yet if I draw  another 690 mm long line it goes way off the artboard. My memory tells me that there is a way that you can set two points and tell Illustrator what the distance between them is, but I'm danged if I can either remember it or find it online. Or am I thinking of another drawing program that I've used in the past?

Thanks in advance,

Bill