The Theolodite

The Instrument

  1. Telescope Objective
  2. Micrometer Knob
  3. Gun sights
  4. Mirror for daylight illumination of readings
  5. Clamping lever for vertical motion
  6. Clamping lever for horizontal motion
  7. Eyepiece of optical plummet
  8. Horizontal fine adjustment
  9. Vertical fine adjustment
  10. Clamping screw
  11. Foot screw
  12. Baseplate
  13. Telescope focus
  14. Eyepiece withreticle focus
  15. Eyepiece of circle reading microscope
  16. Level unit with plate level and pond bubble
  17. Horizontal circle setting knobs, with guard.

Setting Up

The tripod should be set up so that its feet form a roughly equilateral triangle with 1 metre sides. The feet should be pushed firmly into soft ground, or wedged into irregularities (such as cracks) on hard surfaces. The top of the tripod should be level, at about mid chest height for the user.

  1. Grasp two legs and place the tripod roughly central above the set up point, keeping the head level.
  2. Step back and view the tripod, shecking that it is level. If it is not, correct it.
  3. Drop a small stone or coin through the tripod head as a check on its centering.
  4. Place the Theodolite onto the tripod, so that by eye alone it is level and central.
  5. Press the tripod feet firmly into the ground.
  6. Look through the optical plummet.Disregarding the need to level the instrument, use the footscrews to bring the cente of the plummet sight in line with the centre mark of the set up point.
  7. Rotate the instrument so that the plate bubble lies parallel with one side of the triangle made by the feet of the tripod.
  8. By adjusting the length of one or two (not all three) of the legs, centre the plate bubble.
  9. Rotate the instrument through 90'. The Plate bubble should now point to the third leg. Adjust the length of this leg to level the plate bubble.
  10. Turn back through 90', and readjust if necessary.
  11. use foot screws


To efficiently and accurately sight the instrument onto a point, follow these simple steps.

  1. Adjust the instrument to eliminate parallax.
  2. With the clamps open, target the telescope onto the points using the gun sights mounted on top of the scope.
  3. Close the clamps. Look through the 'scope, and using the rapid adjustment screws, bring the target point closer to the centre of the scope. Ensure that the instrument is focused corectly.
  4. Still viewing through the scope, use the fine adjustment screws to centre onto the target.

Reading the Instrument

A theolodite is read by looking into the circle reading microscope, in which you should see this:-

  1. Adjust the focus if necessary by twisting the eyepiece, and adjust the mirror until enough light is reflected into the instrument to allow clear reading.
  2. View the window marked HZ. Adjust the micrometer knob until one of the divisions with a number below it is centered within the two small lines. This number is the Degrees.
  3. Read the minutes and seconds from the middle of the small window on the right. The diagram is a 6 second theodolite, ie it reads to the nearest 6" .

Setting the Instrument

  1. Sight onto the initial point of interest
  2. release the guard lever on the horizontal circle setting knobs.
  3. Depress the smallest knob, and rotate. This allows coarse adjustment of the horizontal circle. Set to close to the required reading.
  4. Apply fine adjustment to the setting by depressing and turning the larer knob.
  5. Having reached the required setting, re-engage the guard lever.

Select Back to return to the Introduction screen.