Focussing
Focussing is essential to eliminate parallax whereas on the staff taking reading. The steps required in focussing are following:
(i) Focussing the eyepiece: in front of telescope hold a sheet of white paper for this and rotate eyepiece in or out until the cross hairs are seen sharp and distinct.
(ii) Focussing the objective: For this telescope is directed towards the staff and until the reading appears clear and sharp the focussing screw is turned.