GB557895A - Improvements relating to computers of the slide rule type - Google Patents

Abstract

557,895. Calculating apparatus. LEVKOVTTSCH, P. GOUDIME-. July 29, 1942, No. 10618. [Class 106 (i)] A device of the sliderule type comprises an ordinary logarithmic scale and a relatively movable reversed logarithmic scale whereby C the value NŒ- may be D read off directly. The reversed or auxiliary scale bears numbers which instead of the actual numbers, are the values obtained by adding or subtracting respectively those numbers from the value of N, the point bearing the value N - 1 being the index of the scale. Additional logarithmic scales may be provided to solve equations of the form A C - y where A is of the form N - - and B of B D C the form N - -. A circular form of slide rule E for determining the value y is shown in Fig. 1. It comprises two concentric relatively rotatable discs 1 and 2; on the lower disc 1 is a main scale 3 viewable through an aperture 5 in the upper disc 2 and an additional logarithmic scale 6; on the upper disc is a reversed logarithmic scale 4 and an additional logarithmic scale 7. Two radially extending arms 8 and 9 called A and B respectively are arranged to rotate about the axis of the discs. In a modified form (not shown) two pointers are mechanically linked to the arms 8 and 9 respectively and co-operate with the main scale 3 to simplify the setting. A form of the device for use in solving problems in air navigation is shown in Figs. 4, 5 and 8, and is based on the four point bearing method of computing the wind speed and direction involving timing the aircraft between intervals during which bearings are taken of a fixed object. From a knowledge of the times T1, T2 and T3, defined in the Specification, the wind angle # can be derived from the equation and the angle of drift o derived from the equation The device comprises five relatively rotatable discs 10, 20, 30, 40 and 50. The upper disc 10 is formed with an arcuate slot 11 and bears an auxiliary scale 12. The disc 20 has a main scale 21 called the time scale and a " Log A and B " scale 22. Beneath the disc 20 is the disc 30 which bears a scale 31 of log. Tan # and to which is secured the "A" arm 32. A portion of the scale 31 is viewable through an arcuate window 42 in the disc 40 on which is formed the " B " arm 41. A window 43 in the arm 41 co-operates with a scale 23 on the reverse side of the disc 20 to read off the drift angle. On the disc 40 is engraved a logarithmic airspeed scale 44 and on the disc 50 is a logarithmic sine scale 51 whereby the wind speed W and the ground speed G can be determined from the airspeed V by the sine formula