Procedure :
1. Set up the instrument over Q and level it accurately with the telescope in the normal position.
2. Set the vernier A to 360o. Loosen the lower clamp direct the telescope to left hand ranging road at P, and bisect it exactly by using lower clamp and lower tangent.
3. The vernier reading should be the same.
4. Loose the upper clamp and truth the telescope in clockwise direction and bisect the right hand ranging road at R exactly by using the upper clamp and upper slow motion screw.
5. Read both vernier. Let the mean reading be 30o 2’.
6. Leaving the vernier unchanged, unclamp the lower plate and turn the telescope in clockwise direction bisect the ranging rod at P exactly with lower clamp and lower tangent screw. The reading on vernier should be same as before.
7. Loose the upper clamp and turn the telescope in clockwise direction and bisect ranging rod at R exactly by using upper clamp and upper tangent screw.
8. The verniers will now read twice the value of angle i.e 2 × 30o 2’.
9. By leaving the verniers clamped at 60o 40’ measure the angle third time.
10. Read both the verniers. Read the final angle.
11. The average angle with face left will be equal to the final reading divided by three.
12. Change the face and make three more repetition as described above.
13. Find the average angle with face right by dividing the final reading by three.
14. By taking average of both the face, horizontal angle PQR is obtained.