A surveyor’s mark cut in some durable material, as a rock, wall, gate-pillar, face of a building, etc., to indicate the starting, closing, or any suitable intermediate, point in a line of levels for the determination of altitudes over the face of a country. It consists of a series of wedge-shaped incisures, in the form of the ‘broad-arrow’ with a horizontal bar through its apex, thus ⍐. When the spot is below sea-level, as in mining surveys, the mark is inverted.
[The horizontal bar is the essential part, the broad arrow being added (originally by the Ordnance Survey) as an identification. In taking a reading, an angle-iron ⦢ is held with its upper extremity inserted in the horizontal bar, so as to form a temporary bracket or bench for the support of the levelling-staff, which can thus be placed on absolutely the same base on any subsequent occasion. Hence the name.]
1864. Webster cites Francis.
1883. G. Symons, Brit. Rainf., 134. A series of levels has been taken from the gauge to an Ordnance bench mark.
