Deviation is the error caused by the sailboat’s own magnetic fields affecting the compass. To calculate it, you compare your boat’s compass heading to a known accurate heading and measure the difference. Basic Formula Deviation=Magnetic Heading−Compass Heading\text{Deviation} = \text{Magnetic Heading} - \text{Compass Heading}Deviation=Magnetic Heading−Compass Heading If the compass reads lower than the magnetic heading → deviation is East. If the compass reads higher than the magnetic heading → deviation is West. Common Method: Compass Swing This is the standard method used on sailboats. Step 1: Choose Calm Conditions Minimal wind/current Flat water Electronics and metal objects in normal operating positions Step 2: Steer Known Headings You steer the boat on several headings: N NE E SE S…