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