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6.6 Finding Latitude and Longitude
Determining the latitude and longitude from a point on the chart is a fundamental skill and is relatively straightforward. The easiest way to determine latitude is to orient the parallel ruler on a horizontal line on the chart and then "walk" the parallel ruler until it meets the point of interest and lines up with the chart's horizontal scale; the latitude can be read from the scale. Longitude can be found in a similar way except that you line up the parallel ruler along a vertical line on the chart.
Photo 6.5.1 shows an example of this process. In order to find the position of black point on the chart, start by positioning the parallel ruler through the horizontal line at 37°58.2'N and then walk the ruler to run through the buoy's position and the horizonal scale. Next, position the parallel ruler through the vertical line at 24°05' and walk the ruler to run through the buoy and the vertical scale. The lines show the position of the buoy to be 37°58.2'N, 024°06.0'E. If the position of interest is further from the edge of the chart than the length of the parallel ruler, you can find the latitude and longitude by employing dividers. Line up the ruler with any vertical or horizontal line on the chart, move to the position to measure, and use the dividers to see how far you are from the line. Then, use the dividers on the vertical or horizontal scale to find the latitude or longitude, respectively.