GB254589A - Improvements in or relating to tabular calculating apparatus particularly for use inthe laying of ordnance - Google Patents

Abstract

254,589. Grotendorst, W. F. Jan. 5, 1925. Logarithmic calculators particularly for use in the laying of ordnance comprise a logarithmic table of angles constituted by a series of rows of equal length, a ruler three times the length of a row and graduated to indicate lengths in accordance with the length of a row, and a tabular arrangement of anti-logarithms for converting lengths read from the rule into the values (e.g range) required. The device is described for use with a gunnery calculator as described in Specifition 254,351. Referring to the diagram shown in Fig. 1, where Z<1> Z<2> represent two observation posts and D the position of a target, the problem is to determine the range Z<2>D from the observed quantities a and # and the known base length b from the equation log Z<2>D = log b + log sin a - log sin t where t = # -a. In the table of angles, part of which is shown in Fig. 2, log sin a and log sin tare indicated on the ruler, Fig. 4, log b is indicated, and in the anti-logarithm or distance table, part of which is shown in Fig. 3, log Z<2>D is obtained. The table of angles is constituted by a number of rows of angles so arranged that all the angles in any row have the same digit for the first decimal of the log sine, the position of the angle in the row being proportional ta the second and third decimal figures of the log sine. A number of rulers are provided depending on the length of base b. One ruler is shown in Fig. 4 and comprises a centre portion with a cursor M, base length scales a, c, and a uniform scale d and scales e, f extending to the right and left similar to the scale d. The graduations a, c are made such that the distances given correspond with the logarithmic divisions in the middle portion d of the scale. The scales d, e, f have marks V, V+1, V-1, V+2, or V-2 as a guide to determine the first decimal figure of the logarithm. Three tables of distances are provided depending on the range. The table of ranges for 4-10 kilometres is shown in Fig. 3, and comprises rows of numbers h representing the second and third decimal figures of log Z<2>D obtained from the table of angles and the ruler, Fig. 4, and columns k of distances corresponding to the numbers, and a column l at the left for indicating the first decimal figure of the said logarithm. An example of the use of the apparatus is given in the Specification.