ANS:C - both levelling and centering are done simultaneously

In the plane table;

1. Levelling
2. Centering
3. Orientation
Levelling is done first and centring and orientation may be done simultaneously as the orientation disturbs centring and vice-versa If you move the tripod stand circumferential then centring position don't change but levelling affected.

If tripod legs moves radially then it don't affect the levelling but centring does. For the Plane table:
1. Levelling
2. Centering
3. Orientation

For Prismatic compass:
1. Centering
2. Levelling
3. Focusing the Prism.