The swing of the lamp and microscope arms can be locked by the two small knobs on the vertical post. When loosened the two units angles can be changed by just grasping any part of either and rotating them.
There is a scale near these knobs which indicates the angle between the light source and the microscope.
With the Topcon unit the scale is under the cover plate used with the fundus lens. It can be removed for normal use when one is interested in the angle between the light source and microscope.
