6.5 in Hilger & Watts SL 10 quickset level with angled mirror to view main bubble. Used for measuring vertical distances between points in conjunction with a levelling staff.
The quickset level is a type of tilting level in which the telescope is not fixed rigidly to the vertical spindle but is capable of a slight tilt. The vertical movement of the telescope is made by rotating a tilting screw just below the eyepiece. Two bubbles are fitted; one, a circular bubble on the upper plate, is designed for approximate levelling, and the other a telescope bubble is levelled for each individual sighting by a tilting screw.