In tacheometric surveying:

a) The intercept of the staff is maximum when the staff is normal to the line of sight.

b) In the tangential system, the staff is kept normal to the line of sight.

c) If a tacheometer is fitted with an anallatic lens, its additive constant is non zero

d) It is more convenient to hold the staff normal to the line of sight than to hold it vertical.

Select the incorrect statement/statements from the above.