Alloy with brass fittings and wooden handle attached to underside.
Index mirror: alloy fixed mount with capstan screw adjustment for perpendicularity.
Horizon mirror: alloy mount. Adjustment in both planes by capstan screws.
Instrument body: alloy rectangular box. Rectangular hole on one side , T-shaped slot at one end and circular hole at opposite end to which is attached a thin brass collar. This aperture is also provided with a sliding bras shutter which houses a peep-hole sight. An alloy lid is provided, to which is attached a hinged brass flap.