World War II-Era World Map Showing Global Magnetic Variation as of March 1940.
Map of the world showing variations of the compass for the year 1940. The map was issued by the United States Hydrographic Office under the Authority of the Secretary of the Navy.
The Variation (magnetic declination) at any place is indicated by the degree-number placed on the curved lines of equal variation of the compass. Easterly variation is denoted by the letter E, and westerly variation by the letter W.
The rate of annual change in variation is indicated by the red curves. Full lines with numbers indicate increasing rate in minutes. Dashed lines with numbers indicate decreasing rate in minutes. Magnetic Observations are indicated in red.
Chart No. 2406.