A. Because, as shown above, the drift alone would require the sight to be set at "Fire left" 12 minutes, and if the wind correction is 6 minutes and is blowing from right to left, to overcome this wind and make the projectile hit the target we would have to "Fire right" 6 minutes. Therefore, if the total setting of the sight is to be "Fire left" 12 minutes plus "Fire right" 6 minutes, the final or resultant setting should be "Fire left" 6 minutes.
Note.—The corrections for wind and drift are usually found at the same time from a chart, correction-board, or table.
Q. Example: The time of flight is 10 seconds (this is found from the gun commander's range-table, knowing the range); how would you determine the correction for travel with a telescopic sight?
A. Set the sight at zero. Traverse the gun until the vertical hair cuts the target. Signal: "Stop traversing," and count the number of seconds time of flight (10), moving by the right hand the deflection-screw, to keep the vertical hair on the target. When 10 seconds are counted stop turning the deflection-screw. Where the vertical hair now rests is the correction for "travel during time of flight." Since to "Fire left" we move the vertical hair to the right, this correction for travel found will have to be set for "Fire left," or on the other side of the scale, if the target is moving from right to left. If it is moving from left to right, the correction found will have to be set "Fire right." In other words, always set the cross-hair in the opposite direction from the motion of the vessel in making the correction for travel. This also applies to open sights.
Q. Example: If you were given the range, a gun commander's range-table, a correction for wind and drift equal to "Fire left" 9 minutes, and the target were moving from right to left, how would you proceed to determine the setting of your sight?
A. First, determine by the above method the correction for travel during time of flight (time of flight being found in the gun commander's range-table). Set this on the sight. Suppose it were "Fire left" 3 minutes.
Second, use this position of the vertical hair as a new zero, and move the vertical hair to "Fire left" 12 minutes. That is, "Fire left" 3 minutes plus "Fire left" 9 minutes equals "Fire left" 12 minutes.
If the travel had been "Fire right" 3 minutes, then by moving the scale "Fire left" 9 minutes, the final setting of the sight would have been "Fire left" 6 minutes.
Q. From the table on page 129 find the number of yards 3 points on the telescopic sight are equal to at 7000 yards range.
A. 18 yards.