Short Answer:

The repetition method in theodolite surveying is a technique used to increase the accuracy of angle measurement by taking the same angle multiple times and then averaging the readings. It helps reduce errors caused by instrument imperfections or human mistakes.

In this method, the telescope is turned back and forth between two points, usually 3 to 6 times. The final angle is obtained by dividing the total measured value by the number of repetitions. This method is commonly used when very precise angle measurement is needed.

Detailed Explanation:

Repetition method in theodolite surveying

The repetition method is a standard procedure in theodolite surveying used to measure horizontal angles with high precision. This method helps reduce random and instrumental errors by measuring the same angle multiple times and taking the average. It is especially helpful when surveying large areas, important boundaries, or during triangulation work where high accuracy is required.

Why use repetition method?
All surveying instruments, including theodolites, may have small mechanical defects or alignment issues. Also, human errors such as wrong readings or improper clamping can affect accuracy. The repetition method balances out these errors by repeating the measurement and averaging the results, giving a more reliable final value.

Steps to perform repetition method:

Setup the theodolite: Place the theodolite exactly over the survey station using a plumb bob or optical plummet. Level it properly using the leveling screws.
Initial sighting (back sight): Aim the telescope at the first point (point A) and set the horizontal angle to zero. Lock the clamps to fix the position.
Turn to second point (fore sight): Rotate the telescope to the second point (point B) and record the angle shown on the scale.
Repetition begins: Without resetting the angle, turn the telescope back to point A and again to point B. Each time you move from A to B, the new angle reading is added to the previous one. Repeat this process 3, 4, or 6 times.
Final calculation: After completing all repetitions, divide the total angle by the number of times it was measured. This gives the average angle between the two points.

Example:
If after 3 repetitions the total angle reading is 180°, then the average angle is 180° ÷ 3 = 60°. This is your final, accurate angle.

Benefits of repetition method:

Increases measurement accuracy
Reduces both instrumental and observational errors
Balances out the effects of gear backlash and improper clamping
Useful for precise engineering surveys

Important tips:

Keep the same face (left or right) during all repetitions to maintain consistency.
Use smooth and careful movements to avoid jerks during rotation.
Ensure the theodolite remains level and properly centered throughout the process.

This method is mostly used in manual (vernier) theodolites, but even with digital instruments, repeating measurements helps verify the results and ensures better reliability in critical surveying tasks.

Conclusion

The repetition method in theodolite surveying is a reliable technique to measure angles accurately by repeating and averaging multiple readings. It helps in achieving high precision, which is essential in boundary surveys, triangulation, and detailed engineering projects.