This article describes studies that evaluate the accuracy of measuring a ship’s heeling angle with an inclinometer. It does so by comparing inclinometer readings with benchmark measurements made with the optical method. The first part of the article describes the measurement station used for gathering measurement data. This station included an inclinometer and a CCD camera, and was used to process digital images incorporating a horizon line to indicate the ship’s heeling angle. The second part of the article describes the data gathering process carried out on a ship at sea. The final part describes a statistical analysis which compares the angular measurements based on an inclinometer with simultaneous optical benchmark measurements.