Figure B-2. Angle of azimuth.

TM 9-258

horizontal and vertical angles and for general

(fig 4-11). Used as an erecting system in elbow and

topographic work.

panoramic telescopes. It erects the image and bends

Aiming point - The point on which the gunner sights

the line of sight through a 90 angle.

Anastigmat - A compound lens corrected for

when aiming the gun. This point is not necessarily the

astigmatism. Angle The amount of rotation of a line

target itself.

Ametropia - Any abnormal condition of the seeing

around the point of its intersection with another,

power of the eyes, such as farsightedness

necessary to bring it into coincidence with the second

line.

nearsightedness

(hypermetropia),

(myopia),

Angle of azimuth - An angle measured clockwise in

astigmatism. An ametropic eye is one which does not

a horizontal plane usually from north (fig B-2). The north

form distinct images of objects on its retina.

used may be True North, Magnetic North, or Y-North

Amici prism - Also called "roof prism" and "roof-

(Grid North).

angle prism." A form of roof prism designed by G. B.

Amici, consisting of a roof edge formed upon the long

reflecting

face

right-angle

prism

Figure B-2. Angle of azimuth.

Angle of convergence - Angle formed by the lines of

incident ray and the refracted ray (fig 2-24).

Angle of elevation - The angle between the line of

sight of both eyes in focusing on any point, line, corner,

site (line from gun to target) and line of elevation (axis of

surface, or part of an object Also referred to as

convergence angle (figs 3-8 and 3-9).

bore when gun is in firing position) (fig B-3). The

Angle of deviation - The angle through which a ray

quadrant angle of elevation is the angle between the

horizontal and the line of elevation. Angle of elevation

of light is bent by a refracting surface; the angle between

plus angle of site equals quadrant angle of elevation.

the

extension

the

path

B-2