Campbell Scientific WINDSONIC 2-D Sonic Wind Sensors - Manual (Page 38)

Appendix A. WindSonic Orientation
Declination angles east of True North are considered negative, and are
subtracted from 360 degrees to get True North as shown FIGURE A-2 (0° and
360° are the same point on a compass). Declination angles west of True North
are considered positive, and are added to 0 degrees to get True North as shown
in FIGURE A-3.
For example, the declination for Longmont, CO (10 June 2006) is 9.67 °, thus
True North is 360 ° ─ 9.67°, or 350.33° as read on a compass. Likewise, the
declination for McHenry, IL (10 June 2006) is ─2.68 °, and True North is
0 ° ─ (─2.68°), or 2.68° as read on a compass.
FIGURE A-2. A declination angle east of True North (positive) is
subtracted from 360 (0) degrees to find True North
FIGURE A-3. A declination angle west of True North (negative) is
subtracted from 0 (360) degrees to find True North
A-2