Level (optical instrument)

The complete unit is normally mounted on a tripod, and the telescope can freely rotate 360° in a horizontal plane.

The surveyor looks through the eyepiece of the telescope while an assistant holds a vertical level staff which is graduated in inches or centimeters.

In 1832, English civil engineer and inventor William Gravatt, who was commissioned to examine a scheme for the South Eastern Railway's route from London to Dover, became frustrated with the slow and cumbersome operation of the "Y" level during the survey work, and devised the more transportable, easier-to-use "dumpy" level,[1][2] so called because of its shorter appearance.

Because the telescope is not fixed to the level adjusting mechanism, the "Y" instrument is assembled and disassembled for each sighting station.

Sighting is done with an assistant surveyor who holds a graduated staff vertical at the point under measurement.

During night time, the dumpy level is used in conjunction with an auto cross laser for accurate scale readings.

A transit level also has the ability to measure both the altitude and azimuth of a target object with respect to a reference in the horizontal plane.

The instrument is rotated to sight the target, and the vertical and horizontal angles are read off calibrated scales[4] In the first chapter of Thomas Hardy's 1887 novel The Woodlanders,[5] the narrator states, "He knew every subtle incline of the ten miles of ground between Abbot's Cernel and Sherton—the market town to which he journeyed—as accurately as any surveyor could have learnt it by a Dumpy level."

In the online game World of Warcraft, there is a quest in Wetlands given by Surveyor Thurdan to retrieve his lost dumpy level.