What is "declination of the compass"

Declination \Dec`li*na"tion\, n. [L. declinatio a bending aside, an avoiding: cf. F. d['e]clination a decadence. See Declension.]

1. The act or state of bending downward; inclination; as, declination of the head.

2. The act or state of falling off or declining from excellence or perfection; deterioration; decay; decline. ``The declination of monarchy.''
   --Bacon.

   Summer . . . is not looked on as a time Of declination or decay.
   --Waller.

3. The act of deviating or turning aside; oblique motion; obliquity; withdrawal.

   The declination of atoms in their descent.
   --Bentley.

   Every declination and violation of the rules.
   --South.

4. The act or state of declining or refusing; withdrawal; refusal; averseness.

   The queen's declination from marriage.
   --Stow.

5. (Astron.) The angular distance of any object from the celestial equator, either northward or southward.

6. (Dialing) The arc of the horizon, contained between the vertical plane and the prime vertical circle, if reckoned from the east or west, or between the meridian and the plane, reckoned from the north or south.

7. (Gram.) The act of inflecting a word; declension. See Decline, v. t., 4.

   Angle of declination, the angle made by a descending line, or plane, with a horizontal plane.

   Circle of declination, a circle parallel to the celestial equator.

   Declination compass (Physics), a compass arranged for finding the declination of the magnetic needle.

   Declination of the compass or Declination of the needle, the horizontal angle which the magnetic needle makes with the true north-and-south line.