You have to observe an included angle with better accuracy than what is achievable by a vernier, you will prefer the method of

ANS:A - repetition

Measurement of Horizontal Angles.

a) Repetition Method: This method is used for very accurate work. In this method, the same angle is added several times mechanically and the correct value of the angle is obtained by dividing the accumulated reading by the no. of repetitions. The No. of repetitions made usually in this method is six, three with the face left and three with the face right. In this way, angles can be measured to a finer degree of accuracy than that obtainable with the least count of the vernier.

b) Reiteration Method. This method is another precise and comparatively less tedious method of measuring horizontal angles. It is generally preferred when several angles are to be measured at a particular station. This method consists of measuring several angles successively and finally closing the horizon at the starting point.