ABAC scale


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ABAC scale

ABAC scaleclick for a larger image
A nomogram for determining the conversion angle to apply when plotting great-circle bearings on a Mercator projection. ABAC scales are printed on the margins of Mercator plotting charts. Scales A and C are interrelated, as are B and D. In the illustration, the ABAC scale measures the conversion angle for two places that have a 16° change of longitude between them and a mean latitude of 50°. The conversion angle in this case is 6°.