Abstract: An instrument is disclosed which comprises a liquid filled casing and a float structure in the casing. The float or floats of the float structure are fully submerged and this structure is mounted for rotation about a horizontal axis. The buoyancy force on the floats tends to return the float structure to a datum position and resist movement from that position. A gear system is provided for converting tilting movement of the casing with respect to the float structure into movement of a counterbalanced needle across a scale, the scale itself being mounted on the float structure. In a further disclosed form, the needle of a lower instrument has the casing of an upper, smaller but otherwise identical instrument secured thereto. In this form proximity sensors are used to detect movement of the needles with respect to the casings. Two floats are preferably employed, these being one to each lateral side of a mounting spindle of the float assembly and above a horizontal plane through the spindle.