TheoNav is a PalmOS application with utilities for aiding in maritime navigation. It is a "Swiss-Army Knife" of (hopefully) useful calculations and references: 1. Includes a basic calculator for speed/time/distance calculations, and handles conversions between english, metric, statute and nautical units. 2. Calculates Great circle distances between two points on the Earth, including the direction from one point to the other. 3. Performs vector calculations of speed and heading when travelling through a current. 4. Determines magnetic variation for any location on the earth. 5. Calculates compass deviation curves, given a set of compass error measurements. Generates a compass deviation table and converts between compass, magnetic and true headings.