Abstract: A two-axis angle sensor comprising a pair of bubble chambers (3,4) and associated bubble detectors (5,6). A processor (42) calculates the angle of the sensor by combining the signals from the first and second bubble detectors in accordance with a predetermined algorithm. A radiation source (1) illuminates a bubble (8) with radiation whereby the radiation is refracted by the bubble. A radiation detector (5,6) is positioned to detect the refracted radiation from the bubble and generate a signal indicative of the angle of the bubble chamber. An angle sensor is used to calibrate a vibrating structure gyroscope (70). A flywheel (91) is provided to generate a gyroscopic resistance to operator input. A method of manufacturing a bubble angle sensor is disclosed, the method employing a lid (61) with an internal recess (65).