DCHP-1 Online
proof line Obs. 
in government surveys, the east-west line that functions as a starting point for the parallel lines demarcating blocks, townships, etc.
See also: base line
- 1810 (1909) I proved every concession line that I ran by measuring on the said proof line, and can safely say that the operation is very correct.
- 1853 He was last seen alive in the Tavern . . . on the Thursday night previous, and in a very intoxicated state left for home by the 8th concession east of the proof-line, across which runs a very dangerous creek.
- 1810 (1909) I proved every concession line that I ran by measuring on the said proof line, and can safely say that the operation is very correct.