line of sight is horizontal

axis of the telescope is horizontal

line of collimation is horizontal

geometrical axis of the telescope is horizontal.

the power of a lens is the reciprocal of its focal length

the unit of power of the lens is diopter

the power of two or more thin lenses in contact is the power of the combination of the lenses

All of these

declination

azimuth

dip

bearing.

bench mark

datum point

reduced level

reference point.

in the objective glass

at the centre of the telescope

at the optical centre of the eye piece

in front of the eye piece.