The difference of level between a point below the plane of sight and one above, is the sum of two staff readings and an error would be produced equal to

thrice the distance between the zero of graduation and the foot of the staff

the distance between the zero of gradient and the foot of the staff

twice the distance between the zero of graduation and the foot of the staff

The difference of level between a point below the plane of sight and o

1.	The difference of level between a point below the plane of sight and one above, is the sum of two staff readings and an error would be produced equal to
A.	the distance between the zero of gradient and the foot of the staff
B.	twice the distance between the zero of graduation and the foot of the staff
C.	thrice the distance between the zero of graduation and the foot of the staff
D.	none of the above.
Answer» C. thrice the distance between the zero of graduation and the foot of the staff