Backsight \Back"sight`\ (b[a^]k"s[imac]t`), 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.
[1913 Webster]