Now move the telescope to the first stake; set up and level the instrument with the objective at the height of the point marked on this stake. Lay on the marked point of the second stake and read the site. This angle will be equal to (300 -S × E). Subtracting one reading from the other we have:—(300 × S × E) - (300 - S × E) = 2S; or one-half the difference of the two readings is equal to the angle of slope of the line of sight. Therefore with the cross wires directed upon the marked point of the second stake, center the bubble of the site level. Now loosen the angle of site locking screw and turn the micrometer to read (300 - S), being careful to keep the bubble centered. Screw up the locking screw. The instrument is now in adjustment. After one telescope has been adjusted, other telescopes, aiming circles and quadrants may be adjusted by merely measuring the site of some distant point. The other telescopes and guns, being in position near the adjusted telescope, are then made to read the proper site when laid upon the distant point. FIELD ARTILLERY RANGE FINDER, 1 METER BASE (Bausch & Lomb.) The instrument and accessories consist of the range finder proper, the tripod mount, the tripod, the adjusting bar, the carrying-case and the storage box. The optical parts of the =range finder= are embodied in a seamless, steel tube (A) covered with canvas and asbestos, to minimize the effects of the change of temperature. The eyepiece (B) is located in the center of the instrument and is equipped with a focusing device graduated in diopters. A soft rubber eye cap is furnished to protect the observer’s eye from shocks and stray light. A ray filter having two sets of glass is operated by a small lever (C) situated to the lower left of the eyepiece housing. [Illustration: _DIAGRAM TO ILLUSTRATE THE GENERAL PRINCIPLE OF RANGE-FINDERS._] The objective openings on the end boxes are opened and closed by means of rotating shutters (D). Buffers (E) are provided on the ends as a protection against shocks. The range finder is of the type known as the fixed base, invert, single coincidence. The magnifying power is 15; actual field of view 50 mils; shortest distance measurable 400 yards. The instrument weighs about 20 pounds. Under favorable conditions and with expert operators the average errors are: 1000 yds. 5 yds. 2000 yds. 15 yds. 3000 yds. 30 yds. 4000 yds. 55 yds. 5000 yds. 90 yds. 6000 yds. 130 yds. 7000 yds. 175 yds. 8000 yds. 225 yds. In practical use under ordinary conditions and with average operators, the errors are three times as great.