BAIRD &TATLOCK (LONDON) LTD. 



3213 

 3213 T Faber's Improved Calculating Rule, boxwood, 21 in. long, with slide spring with digit 



registering cursor, and book of instructions . , . . . . . . . . 110 



3214 s Faber's Demonstrating Rule, with book of instructions 



DESCRIPTION. 



This demonstration rule is 98 in. long. Of this length the scales occupy 79 in. They are therefore distributed 

 in eight times the space occupied on the Faber rules of regular length, the position on either rule, whether long 

 or short, being thus in exact proportion to each other. 



The back of the slide has the scales for sines, logarithms, and tangents. 



Firstly. The scale has been made about f in. longer at each end, this extra length being provided with the 

 object of affording a firmer hold for the cursor when nearing the extremities of the scales. 



Secondly. The sliding cursor has been somewhat lengthened in order to provide a graduated scale, which, 

 as will be seen, is divided into 12 equal parts with the figure o in the centre and graduations to 6 plus and 6 minus 

 respectively, a small indicator being introduced which can be set to any of these graduations. 



'Ihis, it may be mentioned, obviates a troublesome difficulty which has previously existed, whereby during 

 the working of a complicated calculation provisional results, as they were obtained, had to be entrusted to the 

 memory, whereas by the aid of this new digit registering cursor this difficulty is entirely done away with and 

 the various aforesaid provisional results are, as they are arrived at, registered by moving the indicator in the 

 required direction. 



In addition to the improvements above enumerated, this new scale will be found to possess some minor 

 improvements in the marking of the scales, whereby a quicker reading of results is possible. Full particulars, 

 however, will be found in the books of instructions accompanying each rule. 



3215 

 3215 T Calculating Slide Rule, Barnard's Co-ordinate Spiral in mahogany case with book of 



instructions 



This spiral slide rule, which will be found to be of the very greatest possible use to civil engineers and surveyors, 

 is an improvement on our well-known Fuller's rule and is the invention of Mr. H. O. Barnard, of the Surveyor- 

 General's Department, Ceylon. Like Professor Fuller's rule, it enables the user to perform, with speed and 

 accuracy, arithmetical computations involving : multiplication, division, proportion, continuous fractions, 

 roots and logarithms ; but, in addition, the natural and logarithmic values of trigonometrical functions of any 

 angle can be determined by inspection with the same accuracy as in numerical computation, while the products, 

 quotients, etc., of these functions by lengths or numbers, integral or fractional, are obtained with equal ease, 

 rapidity an I precision. 



400 



400 



610 



