benchmark
benchmark a standard or point of reference against which things may be compared or assessed; a benchmark was originally a surveyor's mark cut in a wall, pillar, or building and used as a reference point in measuring altitudes.
The mark consists of a series of wedge-shaped incisures, in the form of the ‘broad-arrow’ with a horizontal bar through its apex; 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.
The mark consists of a series of wedge-shaped incisures, in the form of the ‘broad-arrow’ with a horizontal bar through its apex; 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.
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benchmark