Supposing the range to be estimated at 1,400 yards, the effective zone is about 60 yards in depth--therefore an error of only 30 yards in estimating the range can be permitted. There is but one way to overcome the difficulty, and that is by _increasing_ the effective zone; and this can be done by using “combined sights,” thus making two or more beaten zones which touch each other and overlap where the effective 75 per cent. of shots of both ends. There are two ways of using combined sights: (_a_) The “single gun” method. (_b_) The “battery” method. In (_a_), with an estimated range of 1,400 yards, the sights will be set for 1,300 and aim taken; then the sights will be again set for 1,500 yards, but without altering the original aim, and then “rapid” fire opened and the elevating wheel slowly turned to elevate the gun until the 1,500 yards sighting is aligned on the target. The result of this operation is to sweep the whole ground from 1,270 to 1,530 yards with effective fire; and if an error of 125 yards over or under the correct range has been made, the target is nevertheless brought within the effective zone by the combined elevations used. This is the best method for sections or single guns, and a section can vary this by one gun using 1,250 yards elevation and working up to 1,400, while the other gun begins at 1,350 and works up to 1,550. The choice of the amount over and under the estimated range must depend upon the ability of the person estimating the range and circumstances of the case, but less than 100 yards over or under should never be used. The second method (_b_) is only used where at least four guns are available, and requires six guns to obtain the best results. The range is estimated as before, and then each gun uses an elevation differing by 25 yards from the next: thus, taking 1,400 yards again as an example of the estimated distance, No. 1 gun will use 1,300; No. 2, 1,325; No. 3, 1,350, and so on, No. 6 using 1,425 yards. In this way the effective zone of No. 1 gun, which is 60 yards in depth, will just overlap the effective zone of No. 2 gun, and so on right up to No. 6 gun. Thus instead of one small zone of 60 yards of effective fire, we have six guns joining to make one big effective zone 185 yards deep. Care must be taken not to use more than 25 yards between sights at ranges over 1,400 yards, otherwise there will be gaps between each effective zone, and the fire would be ineffective should the target happen to be at a spot between any two zones. The methods of firing the gun are laid down in the official Handbook, but it may be added that in using “deliberate” fire the double button should be pressed irregularly so as to imitate rifle fire, and with a little practice a rate of 120 shots a minute can easily be attained.