附上原文
DUMARESQ MARK VIII. AD. PATT. No. 5909A
Plate 1
1. The Dumaresq is an instrument which, set with own speed and the relative bearing of the enemy, and her inclination and speed, will calculate the relative course and speed and resolve it into two components-one along the line of sight, i.e., rate of change of range, and the other across the line of sight, i.e., Dumaresq deflection.
Description
2. The Dumaresq consists of a circular frame and on its upper edge from 0° to 180°, Red and Green relative to the Fore an Aft Bar which is mounted on the frame. The frame itself is clamped down with this bar parallel to the Fore and Aft line of the ship.
Under this bar is mounted a slider which travels along a feathered shaft and carrying an index cursor which can be moved aft from the centre a scale graduated from 0 to 35 knots for own speed. This feathered shaft is connected by gearing to the base plate carrying the line of sight arrow and keeps the zero line of inclination plate parallel to this line of sight. The inclination plate is graduated from 0° to 180° right and left, to which is set the inclination of the enemy by an index carried on the Enemy Bar. The underside of the inclination plate is serrated and can be engaged with similar serrations on the upper side of another plate by pressing down on the thumb plate on the top of the slider. This lower plate carries the Enemy Bar.
The Enemy Bar is graduated in knots for speed of enemy from 0 to 35 knots towards the stern and carries on the underside a pointer from which is read off the Rate and Deflection on the base plate. The base plate on which is engraved the line of sight arrow is revolved inside the circular frame by means of a milled wheel. It is inscribed with lines parallel to the line of sight, the distance apart representing 4 knots. Lines at right angles to the line of sight are graduated in 200 yard steps from zero to 2,000 yards opening on the upper half and zero to 2,000 yards closing on the lower half of the plate. A slot is cut at right angles to the line of sight through the centre of the base plate; under the slot a deflection drum is mounted capable of being revolved to a scale of range on the left perimeter and having scribed curves graduated from zero on the centre, out to left and right. The graduations are either in units or knots, depending upon the graduations on the deflection dial of the gun sight. These curves and ranges are applicable only to the gun from whose Range Tables the graduations are calculated. This drum is easily detachable for replacing another drum graduated for a different calibre of gun.
Operation
3. Set own speed on Fore and Aft Bar.
Train line of sight on enemy by open sight or set to relative bearing by means of the milled wheel.
Set enemy speed on Enemy Bar.
Set Enemy Bar to inclination ordered.
Set Range on drum.
Read off on base plate, the Rate on the horizontal lines, indicated by the pointer.
Follow the vertical line directly under the pointer to where it cuts the drum and read off the gun deflection.
Note.-A knot of deflection represents the angular movement of the line of sight to a target which is moving at a speed of one knot across the line of sight during time of flight, the target being at the range for which the deflection dial is graduated. A further explanation is given in B.R. 981, page 11.
In the diagram the pointer is indicating Rate 800 Closing, Gun Deflection 4 Right.
When own ship alters course, press down on the thumb to plate to engage Enemy Bar to slider so that the inclination is kept constant, although the bearing alters. Thumb plate must be released as soon as own ship is steady. It must be remembered that inclination will alter equally with bearing, if neither ship alters course, whereas the angle between keels remains constant.

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