Abney level and clinometer by J.H. Steward Ltd. Circ 1940.
This example of an Abney level and clinometer was manufactured by J. H. Steward Ltd from the registered address of 406 The Strand, London and was manufactured around 1940. It is complete with its leather carry case and is in very good condition. The company of J. H. Steward Ltd was established in 1852 and finally closed its doors in 1975.
An Abney level and clinometer is an instrument used in surveying which consists of a fixed sighting tube, a movable spirit level that is connected to a pointing arm, and a protractor scale. An internal mirror allows the user to see the bubble in the level while sighting a distant target. It can be used as a hand-held instrument or mounted on a Jacob's staff for more precise measurement, and it is small enough to carry in a coat pocket.
The Abney level is an easy to use, relatively inexpensive, and, when used correctly, an accurate surveying tool. Abney levels typically include scales graduated in measure degrees of arc, percent grade, and in topographic Abney levels, grade in feet per surveyor's chain, and chainage correction. The latter is the cosine of the angle, used to convert distances measured along the slope to horizontal distances. By using trigonometry the user of an Abney level can determine height, volume, and grade.
Abney levels are made with square tubular bodies so that they may also be used to directly measure the slopes of plane surfaces by simply placing the body of the level on the surface, adjusting the level, and then reading the angle off of the scale.