Temporary adjustments are a set of operations which are performed on a theodolite to make it ready for taking observations. These include its initial setting up on a tripod or other stand, centering, levelling up and focusing of eyepiece.
Exact centering is done by using the shifting head of the instrument. During this, first the screw-clamping ring of the sliding head is loosened and the upper plate of the shifting head is slid over the lower one until the plumb bob is exactly over the station mark. After the exact centering, the screw clamping ring is tightened. This can be done by means of a forced centering plate or tribrach. An optical or laser plummet is normally used for the most accurate setting. The centering and levelling of the instrument is interactive and iterative; a re-levelling may change the centering, so error each is eliminated successively until negligible.
Leveling of an instrument is done to make its vertical axis adjusted with respect to the apparent force of gravity at the station.
For two spirit vials at right angles:
The same principle applies for a bulls-eye level:
To obtain an accurate clear sighting, the cross hairs should be in focus; adjust the eyepiece to do this.
To clearly view the object being sighted focus the objective lens.
Temporary adjustments are a set of operations which are performed on a theodolite to make it ready for taking observations. These include its initial setting up on a tripod or other stand, centering, levelling up and focusing of eyepiece.
Exact centering is done by using the shifting head of the instrument. During this, first the screw-clamping ring of the sliding head is loosened and the upper plate of the shifting head is slid over the lower one until the plumb bob is exactly over the station mark. After the exact centering, the screw clamping ring is tightened. This can be done by means of a forced centering plate or tribrach. An optical or laser plummet is normally used for the most accurate setting. The centering and levelling of the instrument is interactive and iterative; a re-levelling may change the centering, so error each is eliminated successively until negligible.
Leveling of an instrument is done to make its vertical axis adjusted with respect to the apparent force of gravity at the station.
For two spirit vials at right angles:
The same principle applies for a bulls-eye level:
To obtain an accurate clear sighting, the cross hairs should be in focus; adjust the eyepiece to do this.
To clearly view the object being sighted focus the objective lens.