Patent GB-822420-A (GB)
Title: Improvements in or relating to computing instrument
IPC: G06G5/00
Filed: 1957-08-29
Abstract: 822,420. Calculating-apparatus. GERBER SCIENTIFIC INSTRUMENT CO. Aug. 29, 1957 [Sept. 25, 1956], No. 27219/57. Class 106 (1). Apparatus for analysing graphs comprises a support for a graph, a plate bearing a cursor line and a plate bearing a curve corresponding to a logarithmic function, these three members being relatively movable in a direction perpendicular to the cursor line, and a scale on which may be read a value dependent on the ordinate of the graph at a chosen point when the cursor line is aligned with that ordinate and the logarithmic curve is arranged to intersect the graph at that point. The sheet S bearing the graph G to be analysed is secured on a translucent and internally illuminated table 12 beneath a thin transparent flexible plate 46 bearing the cursor line 48 and carried by a slide 14, and a glass plate 50 bearing the curve 52 pivotally mounted about an axis 62 on a slide 16. The plate 50 is preferably adjustable through a small range in the direction of the cursor line 48 by means of a knob 68, in which case a clamping knob 70 is also provided. The slides 14 and 16 are movable transversely by independent electric motors 36, 38. The curve 52 is actually divided into several sections as shown, these being distinguished by different coloured symbols. The scale 74, (see also Fig. 9), which is carried by a plate 72 movable with the slide 14 and cursor plate 46, is logarithmic and is divided into sections corresponding to those of the curve. For convenience, the scale is actually duplicated, one being arranged beside the other but being shifted so that the sections of one run on to the sections of the other. The scale co-operates with an indicator plate 78 which is movable with the slide 16 and the plate 50 bearing the curve. In use, when it is desired to measure an ordinate of the graph G, the cursor line 46 is aligned with the ordinate and a section of the curve 52 is arranged to intersect the graph at its intersection with the cursor line. The relative movement between the plates 46 and 50 bearing the cursor line and the curve 52 is then a measure (logarithmically) of the height of the ordinate and a corresponding value may be read from the scale 74 by means of the indicator 78 using that section of the scale which corresponds to the section of the curve 52 intersecting the graph at the point under examination. Further by reading the scale against appropriate indicator markings 80, the value corresponding to the ordinate may be multiplied by a selected coefficient. Each of the columns of indicators headed L, A, B, &c., corresponds to a predetermined coefficient and the various indicator markings in each column correspond to the different sections of the curve 52 and are colour coded accordingly. In an alternative arrangement, the indicator markings to be used for a particular curve section are selected by appropriately adjusting an auxiliary indicator plate bearing arrows to indicate the markings to be used. As shown, the coefficients are sine values of chosen angles and the use of the apparatus in determining the unknown values in Fourier equations corresponding to a graph under examination is described. In such an application, the ordinates are measured at equal intervals along the axis of abscissµ for a cycle of the graph and to facilitate this division, an extensible scale in the form of a spring 118 is provided. One end is fixed and the other secured to a slide 116 by which it may be adjusted. The spring has, say, one hundred turns which serve as scale divisions and every tenth one may be distinctively coloured. A pointer 88, adjustably secured to the slide 14 and so movable with the cursor plate 46, cooperates with the scale. Programme forms 89, 90 may be supplied for particular applications to facilitate the tabulation and calculation of results. The application of the apparatus to the analysis of graphs corresponding to power series is also described.