List any four essential characters of Tacheometer.
1. The value of constant f/i = 100 Where, f = focal length i = length of image.
2. The telescope should be powerful, the magnification should be 20 to 30 times the diameter
3. The telescope should be fitted with anallatic lens to have the value of f +c = 0
4. The vision through the telescope should give a clear and bright image at a long distance.
5. The aperture of the objective should be 35 to 45mm in diameter in order to have a sufficiently bright image.