CompassDeviation employs a curve fitting process to construct a compass deviation table from simultaneous compass and magnetic headings which are observed while swinging ship. Angular spacing of the heading observations is not critical and a useful table can be produced with as few as five headings. Rather than the traditional "connect the dots" approach to construction of a deviation table, CompassDeviation implements a least mean squares (LMS) fit of the headings observations to a physical model of compass deviation. This produces a smooth curve of deviation vs. magnetic heading with much reduced sensitivity to measurement errors and with fewer measurements. The deviation table can be plotted on the screen along with the underlying data points to identify outliers or to quickly evaluate compensation adjustments. Multiple tables are supported for sailboats whose deviation varies with heel angle, for operation over a wide range of Latitudes, or for professional adjusters with several clients. While navigating, the table may be accessed to inter-convert magnetic and compass headings.