Hypertext Webster Gateway: "backsight"
From Webster's Revised Unabridged Dictionary (1913) (web1913)
Backsight \Back"sight`\, n. [Back, adv. + sight. ] (Surv.)
The reading of the leveling staff in its unchanged position
when the leveling instrument has been taken to a new
position; a sight directed backwards to a station previously
occupied. Cf. {Foresight}, n., 3.
Additional Hypertext Webster Gateway Lookup
Gateway by dict@stokkie.net
stock only wrote the gateway and does not have any control over the contents;
see the Webster Gateway FAQ,
and also the Back-end/database links and credits.