United States. War Department - 1923 - 1600 pages
...of one angle are perpendicular to the sides of the other, respectively. Because of the fact that an exterior angle of a triangle is equal to the sum of the two opposite interior angles, it follows that — In triangle IHE, IEH+IEH=FIH=a IEH=a-IHE=ab=VIZ. CARE AND ADJUSTMENT OF INSTRUMENTS...