We all depend on our compasses. Even in this age of GPS which locates our positions with pinpoint accuracy and can also determine the direction of our movements, only a compass provides us our basic underlying directional information ... that is, IF we properly understand how to adjust for magnetic variance. With the earth's magnetic field always in motion, accurate adjustment requires accurate magnetic field maps. NOAA and the British Geological Survey recently completed the most current update of their World Magnetic Model (WMM). For a fascinating article on this activity that we boaters all rely on (as do our smartphones and other devices), click the chart below to check it out in Blue Water Sailing's Cruising Compass e-Zine.