---
title: "Temporary adjustments of theodolite"
subject: "Surveying I"
chapter: 7
key: "semester_3/surveying_i:temporary-adjustments-theodolite"
source: https://www.bctengineer.com/q/semester_3/surveying_i/temporary-adjustments-theodolite
site: BCT Engineering
---

# Temporary adjustments of theodolite

Surveying I · Chapter 7: Transit and Theodolite

- Asked in: 2075 Asoj, 4 marks; 2074 Chaitra, 4 marks; 2066 Jestha, 7 marks; 2069 Chaitra, 8 marks; 2074 Asoj, 4 marks; 2062 Baisakh, 8 marks; 2061 Baisakh, 8 marks; 2057 Chaitra, 6 marks (asked 8 times)
- Video: [Part-2 Temporary Adjustment of Theodolite In Hindi (Centering, Leveling, Focusing )](https://www.youtube.com/watch?v=Hl8lyV0op1U) — CE Quick Solution
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/surveying_i/temporary-adjustments-theodolite
- Whole chapter: https://www.bctengineer.com/md/semester_3/surveying_i/chapter-7

## Question

Explain the temporary adjustments of a theodolite.

## Short answer

Temporary adjustments: centering over the station with plumb bob/optical plummet, levelling the vertical axis by centering the plate bubble with foot screws (first parallel to two, then the third), and removing parallax by focusing eyepiece then objective until cross hairs and image do not move relative to each other.

## Answer

The temporary adjustments are the operations done at every set-up of the theodolite, before any angle is observed. They are done in this order:

#### 1. Setting up the theodolite over the station
- Spread the tripod legs so that the head is at about chest height and roughly level, with the plumb bob (or optical plummet) near the station mark.
- Fix the instrument on the tripod head with the central fixing screw.
- Adjust the legs (move one leg in or out, or shift all the legs together) until the plumb bob is vertically above the station mark. This is **centering**. Fine centering is done by loosening the fixing screw and sliding the instrument on the tripod head.

#### 2. Levelling up
The vertical axis is made truly vertical using the plate levels and the three foot screws.

1. Turn the upper plate until the plate level is parallel to the line joining any two foot screws.
2. Turn those two screws together in opposite directions (thumbs moving towards or away from each other) until the bubble is central.
3. Turn the instrument through 90 degrees so that the level points towards the third foot screw, and bring the bubble central using that third screw only.
4. Return to the first position and repeat. Continue until the bubble stays central in every position of the instrument (check by turning it through 180 degrees and through a full turn).

Levelling can disturb the centering slightly, so check the plumb bob again.

```text
   Foot screws: A, B, C         Step 1: level || AB
                                Step 2: turn 90 deg,
                                use C only
        A ---- B                Repeat until bubble stays
          \  /                  central everywhere
            C
```

#### 3. Elimination of parallax
Parallax is the apparent movement of the image relative to the cross hairs when the eye is moved. It is removed in two steps:

1. **Focusing the eyepiece:** point the telescope at the sky or hold a sheet of white paper in front of it, and turn the eyepiece until the cross hairs appear sharp and black.
2. **Focusing the objective:** sight the object and turn the focusing screw until the image is sharp and lies exactly in the plane of the cross hairs.

If the cross hairs and the image do not move relative to each other when the eye is moved slightly, the parallax has been removed.

After these three adjustments the instrument is ready for observation.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the order of temporary adjustments?
   A. Levelling, parallax, collimation
   B. Parallax, centring, adjusting level axis
   C. Setting up (centring), levelling up, elimination of parallax
   D. Setting up, collimation, index error
   Answer: C. They are done at every set-up before observing. (Key point: Order)

2. How is levelling done with the plate level?
   A. Use the third screw first, then the other two together at 180 degrees
   B. Use only one screw
   C. Use the tangent screw
   D. Level parallel to two foot screws, turn 90 degrees, use the third screw, repeat
   Answer: D. The two screws are turned in opposite directions, then the third screw alone. (Key point: Levelling procedure)

3. What is parallax?
   A. Apparent movement of the cross hairs against the image when the eye moves
   B. Error in the vertical axis
   C. Error in graduation
   D. Tilt of the tripod
   Answer: A. It occurs when the image is not in the plane of the cross hairs. (Key point: Parallax)

4. How is parallax eliminated?
   A. Focus objective first on the sky
   B. Focus the eyepiece on sharp cross hairs, then focus the objective on the object
   C. Adjust foot screws
   D. Tighten the clamp
   Answer: B. Eyepiece first, then objective. (Key point: Removing parallax)

## Related in Surveying I

- [Temporary adjustments; fundamental lines](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Atemporary-adjustments-and-fundamental-lines) — Surveying I, chapter 7