Although tefillin is technically the plural form (the singular being tefillah), it is loosely used as a singular as well. The arm-tefillin, or shel yad, is placed on the upper arm, and the strap wrapped around the arm/hand, hand and fingers; while the head-tefillin, or shel rosh, is placed above the forehead.
Definition of declination. 1 : angular distance north or south from the celestial equator measured along a great circle passing through the celestial poles. 2 : a turning aside or swerving. 3 : deterioration moral declination. 4 : a bending downward : inclination.
In other words, declination is the angle between where a compass needle points and the true north pole. If the compass needle points west of true north, this offset is designated as west declination. The world standard, including in the southern hemisphere, is in reference to the magnetic north (MN) declination.f the compass needle points west of true north, this offset is designated as west declination. The world standard, including in the southern hemisphere, is in reference to the magnetic north (MN) declination.