What is Direct method of measuring the angle

Set up, center and level the theodolite at ground point B.
Loosen the top plate, set the vernier to read zero and clamp the top plate.
Loosen the lower plate and swing the telescope until the left point A is visible. Tighten the lower clamp. The correct bisection of the arrow placed at station A is done using the lower tangent screw. Read both the verniers and interpret the readings.

Open the top plate and swing the telescope clockwise until point C is brought into the field of view. Tighten the upper clamp and accurately bisect the arrow at station C using the upper tangent screw.
Read both the verniers and interpret the readings. The difference of the means of the readings of stations C and A is the required angle ABC.
Change the device face and repeat the whole procedure. The angle measurement is recovered by taking the difference of the means of the readings at C and A on the right side of the face.
The product of the two measures of the angle ABC on the two faces is the required angle ABC.