SECTION VI: INSTRUMENTS AND ACCESSORIES

• 18. FIELD GLASS, TYPE EE.—a. Description.— (1) The field glass, type EE (fig. 5), is an observation instrument of 6- power with an 8° field of view. It contains a graduated mil scale for the measurement of small horizontal and vertical angles. In field glasses of older manufacture an inverted sight leaf scale is also provided for the rapid computation of certain fire data. The field glass complete consists of the glass and its carrying case and neck strap. (2) The field glass proper consists of two compact prismatic telescopes pivoted about a common hinge which permits ad adjustment for interplanetary distances. A scale graduated every 2 millimeters from 56 to 74 permits the observer rapidly to set the telescope to suit his eye distance when the spacing of his eyes is known. The eyepiece can be focused independently for each eye by screwing in or out. Each is provided with a dipterous scale for rapid setting when the observer knows the correction for his eye. The zero graduations indicate the settings for normal eyes. (3) The left telescope is fitted with a. glass reticle (figs. 6 and 7) upon which are etched a vertical mil scale, a horizontal mil scale, and on field glasses of older manufacture, a stadia scale graduated similar to the sight leaf graduation on the service rifle, but inverted. 6. Use.—The field glass is used for observations and the measurement of small horizontal and vertical angles in mils. The inverted sight leaf, when provided, is used to pick up auxiliary aiming points in direct laying and to determine troop safety for overhead fire. c. Adjustments.— (1) Interpupillary distance.—To adjust the glass so that the eyepieces are the same distance apart as the pupils of the observer's eye, point the glass at the sky and open or close the hinged joint until the field of view ceases to be two overlapping circles and appears to be one sharply defined circle, then note the reading on the scale which indicates the spacing of the observer's eyes. Similar setting of any other field glass will then accommodate his
• (2) Focus of eyepieces.—Look through the glasses, both eyes open, at an object several hundred yards away. Place the hand over the front of one telescope and screw the eye piece of the other in or out until the object is defined sharply. Repeat this operation for the other eye, then note reading on each diopter scale. Similar reading of any other field glass will accommodate the same eye.
• d. Operation.—(1) In using the glass it should be held in both hands, lightly pressed to the eyes so as to keep the relation with the eyes constant but not so as to transmit tremors of the body. The bent thumbs may cover the cor ners of the eyes to exclude light except that which enters the glass through the lenses. When possible, it is best to use a rest for the glass or to rest the elbows on some solid object.
• (2) The mil scales are seen when looking through the glass and by superimposing them on any objects, the horizontal and vertical angles between these objects may be read.
•  (3) The inverted sight leaf scale is used to secure range settings on sharply defined auxiliary aiming points when the target is not clear enough for direct aiming.
•  e. Care.—The field glass is a rugged, serviceable instrument but it should not be abused or roughly handled. Care should be taken not to scratch or mar the lenses.
• 19. LENSATIC COMPASS, MODIFIED PRISMATIC TYPE.—a. Description.—This compass is an instrument of unusual flexibility and precision when properly used. It has a pivoted dial needle in-closed in a nonmagnetic metal case with a hinged cover and an eyepiece containing a small magnifying lens. The needle dial has inscribed on it two azimuth circles of 6,400 mils, one with its zero at the north point for use in reading the face of the compass, the other with its zero at the south point for use in reading azimuth through the eye piece (fig. 8). The least reading of the compass is 20 mils. Owing to the sensitive character of the needle suspension, even this accuracy is difficult to obtain unless the compass rests on a solid support. One outside ring about the base of the compass is graduated into the cardinal points of the compass and another as an azimuth circle. The former is useful for taking bearings and the latter is useful on a map as a protractor and in setting off azimuth by means of the index on a movable ring about the top. Directions are laid off by means of the index (pointer) on this movable ring. The index on the movable ring, the zero point on the azimuth circle on the dial, and the north point of the needle are marked with radiolite for visibility in the dark. The eye piece consists of a metal standard supporting a small lens through which azimuth may be read directly from the outer dial circle. Vertically above the aperture of the standard is a narrow slit. Vertically across the glass face of the com pass cover is an etched line in the line of collimation of the instrument.
• B. Use.— (1) The chief use of the lensatic compass, modified prismatic type, with the gun is the measurement of magnetic azimuths. It may also be used as a marching compass. 
• (2) If practicable, the compass should be rested on a level surface. However, it can be read accurately when held in the hands, the ring between thumb and forefinger of one hand, the other fingers closed, with thumb and forefinger of the other hand grasping the compass box and the other fingers clasping the other hand, elbows close to the body or resting on the knees, depending on the position of the observer.
•  (3) The instrument should be held as nearly level as possible to permit the dial to swing free, otherwise errors in the readings will result. 
• c. Operation of compass.— (1) To decimate compass.— (a) Select some point located on the map from which several points can be seen, the grid Y azimuth of which can be de termined from the map. Measure the magnetic azimuths (readings from magnetic north) to each of the points and compute the differences between magnetic azimuths as meas ured by the instrument and the grid Y azimuth taken from the map. The average of these differences will be the declina tion constant for that particular compass. Record the value of the constant for ready reference. If the compass is to be used in another locality 6 miles or more distant, the declina tion constant should again be determined for the new locality. 
• (b) In determining the declination constant it is best to select three points, one of which should be at least 2,000 mils from one of the other points.
• (e) If the compass azimuths are greater than the grid azimuths, the declination is west and must be added to grid azimuths to convert to compass azimuth; if less, the declina tion is east and must be subtracted.
•  (2) To measure an azimuth.— (a) Raise eyepiece and cover vertically and lower needle dial. 
• (b) Grasp the ring between thumb and forefinger, allow ing base of compass to rest on the back of the fingers. 
• (c) Hold compass horizontally in front of the face, hand against chin, and aperture of eyepiece immediately in front of one eye with the other eye closed.
• (d) Turn about carefully until the object whose azimuth is desired is bisected by the etched line on the cover as viewed through the slit of the eyepiece standard. Allow needle to come to rest, then read the azimuth from the outer circle as viewed through the aperture. If greater stability of the needle is desired, the compass should be supported on a solid platform or used in a prone position on the ground.
•  (3) To measure an azimuth at night.—(a) Use the radiolite marker on the movable index ring to lay off the azimuth on the circle about the outside of the compass case. The clamp controls the movable ring. 
• (b) Hold the compass horizontally and carefully turn about until the needle points to the marker on the movable ring. The azimuth is now indicated by the radiolite marker along the line of sight of the instrument.
•  (4) To determine azimuth of position of observer from a given point (target).—Read azimuth of given point as de scribed above. Since the position of the observer with re spect to the given point is on back azimuth determine the back azimuth, that is, if the reading is less than 3,200 mils, add 3,200 to it; if over 3,200 mils, subtract 3,200 mils from it. 
• (5) To lay off a line of a given azimuth from position of observer.—Turn compass until the dial index indicates the given azimuth. Direct the placing of an aiming stake on the line of sighting. 
• (6) Given an azimuth to a point, to find a position from which the point is on that azimuth.—The observer places him self approximately on the required line, aims at the given point, and reads the dial. He then moves to right or left while aiming at the point until the given azimuth is indicated on the dial. Moving to the right decreases the reading; to the left increases it.
•  (7) Given the azimuth from a faint, to find a position which is on that azimuth from the given point.—Determine the back azimuth. The result is the azimuth of the given point from the required position, then proceed as in (6) above to find that position. 
• (8) To find the horizontal angle between two points from position of observer.—Read the azimuth to each point and subtract the smaller reading from the larger. The difference is the required angle.
•  d. Care and preservation.—The instrument contains a deli cately pointed pivot and jewel and must be handled care fully. Care should be taken to prevent damaging the glass cover. No adjustments of the parts in the compass box are permitted within the company. 
• • 20. PRISMATIC COMPASS.—This compass is identical in oper ation and construction with the lensatic compass, modified prismatic type, except— 
• a. The needle dial of the prismatic compass is graduated in degrees instead of mils. 
• b. The prismatic compass, as its name indicates, is pro vided with a prism which magnifies the figures on the needle dial instead of the magnifying lens described above for the lensatic compass. 
•  21. TELESCOPIC SIGHT, M1916, FOR THE 37-MM GUN, M1916.— The telescopic sight, M1916, complete, consists of the sight and its carrying case. It is of the fixed focus, straight tele scopic erecting type, 
• a. Description.—The following parts are shown in figure 9.
•  (1) Bracket (6) for attaching the sight to the left side of the gun. 
• (2) Eyepiece (2) which carries the eyelens and is of fixed focus type.
• (3) Eyeshield (1) made of soft rubber, the purpose of which is to shut out light between the eye and the eyelens, and to locate the eye at the proper distance from the eyelens.
•  (4) Sunshade (3) which slips over the front end of the sight to prevent the entrance of the sun's rays to the object lens.
•  (5) Range dial (5) graduated in 50-yard divisions from zero to 1, and in 25-yard divisions from 2 to 18, and numbered every 100 yards.
•  (6) Deflection dial (4) graduated into 140 equal spaces, each space representing an angle of 1 mil and numbered every 10 spaces from zero to 70 clockwise and counter clockwise. b. Use.—The telescopic sight is used for direct laying of the gun. c. Operation.—When the eye is placed at the eyeshield, cross lines appear in the field of vision. One line is hori zontal and the other inclined to the right of vertical 2° 10'. The cross lines are commonly known as cross hairs. The horizontal line is controlled by the range dial. Setting a number on the range dial opposite the index on the body of the sight lowers the line of aim through an angle which is equivalent to the angle of elevation required on the gun for firing at the range corresponding to the number opposite the index. The vertical line is controlled by the deflection dial. Turning the zero graduation of the deflection dial upward toward the word "right" stamped on the body of the sight will set off right deflection in mils as indicated by the graduation opposite the index on the body of the sight. Turning the zero graduation downward sets off left deflection.
• d. Care and preservation.— (1) The dovetail lug cm the bracket should not be damaged, burred, or nicked in such a way as to make the assembling of the sight to the carriage bracket difficult. (2) Wiping dirt or moisture from the eyelens or objective lens should be done carefully with a soft cloth. (3) Before inserting the instrument into the carrying case remove both the eyeshield and the sunshade. Place the instrument in the case, with the eyelens downward, and insert the shield in the space at the side of the instrument with the shade inside the shield.

22. QUADRANT SIGHT, M1916, FOR 37-MM GUN, M1916.— The quadrant sight, M1916, complete, consists of the sight and its carrying case. a. Description.—The following parts are shown in figure 10: (1) Bracket (2) for attaching the sight to bracket on left side of the gun. (2) Housing (3) pivoted on the bracket. The housing bearing is inclined 2° 10' which has the effect of turning the sight line through the collimator to the left, auto matically correcting for drift for the various ranges when the gun is elevated. (3) Collimator (5) mounted on top of the housing is pivoted at its forward end and can be rotated horizontally by turning the deflection dial. (4) Bear lens (4) which magnifies the cross lines on a lens in the front end of the collimator. (5) Deflection dial (6) graduated into 180 equal spaces, each space representing 1 mil and numbered every 10 spaces from zero to 90 clockwise and counterclockwise. Due to con struction the usable range of the dial is limited to 80 mils clockwise and counterclockwise. When the deflection dial is rotated to any desired setting the line of sight through the collimator has been displaced to the right or left through an angle of the value indicated. (6) Range dial (1) graduated in 25-yard divisions from zero to 1,800 and numbered every 100 yards (final 00 is omitted). This dial is also marked to indicate ammunition and fuze for which it is graduated.

(7) Angle-of-site dial (8) rotates independently of the range scale. A portion of the periphery is graduated into 140 equal spaces, each space representing 1 mil and num bered every 10 spaces from zero to 70 clockwise and counterclockwise. (8) An index line engraved opposite the zero graduation of the angle-of-site dial in such a manner as to indicate on the outer edge of the range scale. (9) Level vial (7) for determining the horizontal where indirect laying is used.

b. Use.—The quadrant sight, M1916, is used for aiming the gun in direction by using the collimator and in elevation by using the graduated dials. c. Operation.— (1) For indirect laying rotate the deflection dial until the graduation corresponding to the desired de flection is opposite the upper index on the housing. Rotate the angle-of-site dial until the graduation corresponding to the angle of site of the target is opposite the lower index on the housing. Rotate the range dial until the graduation corresponding to the desired range setting is opposite the index or zero on the angle-of-site dial. Bring the level bubble midway between the graduations on the level vial by means of the elevating mechanism of the carriage, and by means of the traversing mechanism traverse the carriage until the vertical line in the collimator is laid on the aiming point. Check and recenter the bubble if necessary.

(2) For direct laying set the deflection dial at the desired setting, the angle-of-site dial at zero, and rotate the range dial until the desired range IS opposite the index on the angle-of-site dial. By means of the elevating and traversing mechanism of the carriage bring both of the collimator cross lines on the aiming point.

d. To use collimator.—Hold the eye approximately 10 inches in rear of the rear lens. Move the head vertically or hori zontally until the eye views the cross and the target in coin cidence, first in elevation and then in azimuth. It may be more convenient for some men to sight with both eyes open. 

e. To adjust range scale.—Level the gun by using a clinometer and rotate the range dial until the level bubble is midway between the index lines on the level vial. Set the angle-of-site dial at zero. Loosen the range dial securing screw and rotate the range dial until the zero coincides with the index, then tighten the screw. If the bubble has not been displaced from its previous setting during this operation, the sight is in adjustment for range. No means are provided for adjusting the deflection scale in the field. 

F. Care and preservation.—The dovetail lug on the bracket should not be damaged, burred, or nicked in such a way as to make the assembling of the sight to the carriage bracket difficult

23. ACCESSORIES.—a. The accessories for the gun are listed in Standard Nomenclature List No. A-7. The principal acces sories used by the gun crew consist of— (1) Accessory and spare-parts case made of russet strap leather with a buckled cover and fitted straps for fastening to the gun carriage. (2) Ammunition chest made of wood having a hinged cover and spring latch. It holds 16 rounds. (3) Cleaning brush and rammer.—The cleaning brush con sists mainly of a block of wood cylindrical in shape with bristles attached lengthwise about the front outer surface. The rammer which serves as a handle for the cleaning brush is also used to remove a shell from the bore. (4) Drag rope vfith shoulder strap used to move the gun into position by hand. (5) Flash hider, a long metal cone which clamps to the muzzle end of the barrel to cover the flash. (6) Gun cover made of olive-drab duck and provided with leather straps for fastening on the gun. b. Other accessories.—Hand cartridge extractor, oiler, re coil cylinder dismounting wrench, recoil cylinder filling oil gun, and tool roll. Their use is implied by their names.