The theodolite in principle
Measurement - a telescope provides for focal location between instrument and subject. Position of the scope is defined by an index of angles. The scale and presentation of angles varies from traditional micrometer readings to computer compatible crystal displays. Angles are measured in degrees, minutes and seconds, e.g. 165º 53' 30''
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Direct reading micrometer scale
Application - at least two sightings are taken and the readings averaged. After the first sighting, the horizontal plate is rotated through 180º and the scope also rotated 180 through the vertical to return the instrument to its original alignment for the second reading. This process will move the vertical circle from right face to left face, or vice-versa. It is important to note the readings against the facing † see below.
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