If altitude bubble is provided both on index frame as well as on telescope of a theodolite, then the instrument is levelled with reference to

i)    altitude bubble on index frame
ii)   altitude bubble on index frame if it is to be used as a level
iii)   altitude bubble on telescope
iv)   altitude bubble on telescope if it is to be used as a level The correct answer is
a)    only (i)
b)    both (i) and (iv)
c)    only (iii)
d)    both (ii) and (iii)

Ans: b