Mounting arrangement for an inertial measurement unit

In a mounting arrangement for an instrument, such as an inertial measurement unit, a mounting frame is pivotably mounted to a platform for rotation about a vertical axis and a support frame is rotatably mounted to the mounting frame for rotation about a horizontal axis. The support frame supports the instrument. A horizontal lock and motion assembly interconnects the mounting frame and platform, and allows adjustment of the angular position of the mounting frame about the vertical axis relative to the platform when the mounting frame is locked to the platform. A vertical lock and motion assembly interconnects the support frame and mounting frame, and allows adjustment of the angular position of the support frame about the horizontal axis relative to the mounting frame when the support frame is locked to the mounting frame.