Section 1. Preparation and Sitinggeneral map showing magnetic declination for the contiguous United States isshown in Figure 1.5-1.Declination angles east of True North are considered negative, and are subtractedfrom 0 degrees to get True North as shown Figure 1.5-2. Declination angles westof True North are considered positive, and are added to 0 degrees to get TrueNorth as shown in Figure 1.5-3. For example, the declination for Logan, Utah is13.80° East. True North is 360° - 13.80°, or 346.2° as read on a compass.* Other methods employ observations using the North Star or the sun, andare discussed in the Quality Assurance Handbook for Air PollutionMeasurement Systems, Volume IV - Meteorological Measurements4 .Subtract declination from 360° Add declination to 0°22 E18 E16 E14 E12 E10 E 8 E 6 E 4 E 2 E02 W4 W6 W8 W10 W14 W12 W16 W18 W20 W20 EFIGURE 1.5-1. Magnetic Declination for the Contiguous United States1.5.1 NSSDC CGM ServiceThe NSSDC CGM (Corrected Geomagnetic) Service provides an easy way ofdetermining magnetic declination of a specific site. Since magnetic declinationfluctuates with time, it should be determined each time the wind vaneorientation is adjusted. It can be accessed on the world wide web athttp://nssdc.gsfc.nasa.gov/space/cgm/cgm.htmlIf you know the latitude and longitude of your site, fill out Form 1 for anaccurate magnetic declination. Below is an example for Logan, Utah U.S.A.If you do not know the latitude and longitude of your site, fill out Form 2 forestimate of magnetic declination. Note that longitude is expressed in 0 to 360degrees east of the Greenwich prime meridian, and that north latitudes arepositive.A table containing similar information to the following will be returned latersubmitting Forms 1 or 2.1-7
