Patent GB-191327583-A (GB)
Abstract: 27,583. Barr, A., and Stroud, W. Dec. 1 Modifying scale of readings.-Relates to means for indicating the correct tangent angle of elevation to be imparted, or for imparting the correct tangent angle of elevation, to a gun for varying altitudes of the target, and consists in employing, in connexion with rangefinders or gun-sights, a scale so constructed that, by a shift of the pointer co-operating with it, allowance can be made for the effect of changes in altitude. The scale is constructed from a table of tangent elevations for a variety of ranges and altitudes. Two altitudes are chosen, and the scale is so marked that the distance between the graduations corresponding to the tangent elevations for the two altitudes is the same for all ranges of the target. The method adopted may be that of Specification 5182/12, [Class 106 (i), Calculating &c.], The resultant scale is approximately logarithimic, and is such that, by shifting a co-operating pointer, the scale may be converted from one of tangent elevations for one altitude to that for another. The scale may be graduated in ranges by substituting for each tangent elevation the corresponding horizontal range. Such a scale, with a pointer moving in accordance with altitude of target may be employed in conjunction with a rangefinder for indicating the modified " ranger " to be set upon a gun-sight range-scale for any altitude of target. In Fig. 2, A shows the scale, and D a weighted drum turning freely on an horizontal axis. The scale and its carrier are adapted to move in altitude round the axis of the drum in conformity with the range-finder. A curve is drawn on the drum by choosing a mean range (say 3000 yards) and, as the scale moves with the range-finder, into position corresponding to various altitudes, making marks on the drum opposite the scale graduations corresponding to the modified " ranges " for those altitudes, i.e., the horizontal ranges (obtained from a table) corresponding to the tangent elevations for those altitudes. Then, if a fixed pointer is arranged in coincidence with the line when the range-finder altitude is zero, the modified " range to be set off on the gun-sight range scale will be indicated by the intersection of the curve with the scale, when the scale has been moved, parallel to the axis of the drum so that the true range is indicated against the fixed pointer, and the range-finder has been laid on the target. The line on the drum may be replaced by a movable pointer controlled by a pendulum device, or the pointer may be fixed and the scale movable by a pendulum device. The motion of the scale to set it for different ranges of the target may be produced automatically by the operation of the measuring mechanism of the range-finder acting through a cam, or mutilated rack, as described in Specification 29,870/12. In this case the modified " range " to be set on the gun-sight is merely indicated on the scale. Alternatively, this motion may be produced in a similar way by the operation of the range adjusting mechanism of the gun-sight, the arrangement in this case being such that, when the sight is layed on the target, and the range adjusting mechanism is operated until the known range of the target stands opposite the curve of the pendulum drum D, the correct tangent elevation will be imparted to the gun for the particular altitude concerned.