581,905. Correspondence control systems. BURT, F. S., and WRIGHT, C. S. July 17, 1943, No. 11682. [Class 40 (i)] [Also in Group XIX] A calculator for vector problems comprises a pair of relatively slidable members each carrying a a member rotatably mounted at its edge and, having a radial slot formed therein, and a plunger adapted to engage both the slots at their point of intersection, the plunger and centres of the rotary members thus defining the vector triangle. The invention is of particular use in connection with the launching of aircraft, from carriers or from other ships using a catapult, for finding true wind in terms of ship's speed and course and relative wind speed and direction. As shown in Figs. 5 and 6, two rectangular plates 1, 2 are arranged to slide one over the other ; in the centre of the upper plate 1 is a rotatable disc 3 with a radial slot 4 graduated to represent the relative wind vector, the disc being mounted at its edge within a circular aperture in the plate. On the underside in the plate 2 is mounted a disc 6 with a radial slot 7 graduated to read the true wind vector. Surrounding the disc is a loose ring 8 with a scale of degrees to set the bearing angle with respect to an index 16. A pointer 5 adjusted by a knurled knob can slide in the slot 7 and is provided with a spring-loaded plunger 5a that can enter into engagement with the slot 4. Raising the plunger and rotating it through 90 degrees disengages it from the slot 4. In use, the instrument is set by sliding the plates until the ship's speed is set on the scale 9 in plate 1, the centres of the discs being displaced by that amount. The disc 3 being free is rotated to set the direction of the wind on the scale 13. Without turning the instrument over, the disc 6 is rotated until the plunger 5a clicks into the slot 4 and an index thereon is set to the amount of the relative wind on scale 15. The instrument is then turned over and the bearing ring 8 rotated to show the ship's course against the index 16. The true wind and direction is obtained against the index on scale 14 and index on slot 7. A wind component bar 11 slidable on the plate 1 when brought to bear on the plunger 5a gives the wind component across and along the ship. A transparent panel (not shown) is provided, engraved with a rectangle representing the safety limits for launching as regards these wind components, for various classes of ships and enables the minimum changes of ship's course and or speed to bring the readings within the limits. An arrangement whereby the data is transmitted automatically to the calculator is shown in Figs. 7 and 8. In this arrangement the disc 3 is set in accordance with the relative wind direction by a follow-up motor 17 geared thereto and to the resetter 18 of a self-synchronous system controlled by a wind vane. In the slot 4 of the disc is a block A on a quick-threaded screw 19 driven by a motor 20 arranged to follow the movements of a sensitive voltmeter 21 governed by an anemometer measuring the relative wind speed. A follow-up motor 23 operated by the ship's log sets the plate 2 relatively to the plate 1 in accordance with the ship's speed. The adjustment of the disc 6 is controlled by a plunger 5a on the block A co-operating with contacts X and Y on a block B carried by a quick-threaded screw 26 in the slot 7. The contacts X control a followup motor 27 to drive the screw 26 and the contacts Y control a follow-up motor 25 to rotate the disc 6. Transmitters 28, 29 may be employed to communicate the true wind speed and direction to remote indicating or control apparatus. The data may be read on scales provided on the disc 6 and bearing ring 8, the latter being operated by a drive 30 from the ship's gyro compass.