'bench-mark

    a. 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.]
 
  1842 FRANCIS Dict. Arts, Bench marks, in surveying, fixed points left on a line of survey for reference at a future time, consisting of cuts in trees, pegs driven into the ground, etc.1883 G. J. SYMONS Brit. Rainf. 134 A series of levels has been taken from the gauge to an Ordnance bench mark.
 

    b. transf. and fig. A point of reference; a criterion, touchstone.
 
  1884 Science IV. 202/1 These star-places..are the reference-points and bench-marks of the universe. 1957 R. K. MERTON Student-Physician III. 195 Standards represent ‘benchmarks’ with which students compare their ability and performance. 1963 Economist 18 May 663/2 Foreign firms have failed to get..orders unless they have offered a price advantage of at least 50 per cent. This is the ‘bench~mark’.
 

Source: Oxford English Dictionary, 2nd Edition, 1989.