4 WRIGHT: SOLUTION OF EQUATION A=B-C 



the horizontal line through this point intersects the ordinate 

 scale on the right at 25° which is the desired value of A. 



To save time it is well to prepare at the outset pairs of scales 

 of all the trigonometric functions, of logarithms, of reciprocals 

 of numbers, their squares and square roots, and of any other 

 functions which may be employed. Such scales are then always 

 ready for use. 



In case the observer has only a few types of the general equa- 

 tion to solve it is convenient to plot the scales for each type of 



Fig. 5. Device for graphical solution of equation A = B C. 



equation along the sides of a large sheet of coordinate paper, 

 which then serves directly for the solution of the given equation. 

 The bother of adjusting the scales to the sides of the plot is thus 

 eliminated; a special sheet of coordinate paper is, however, 

 required for each equation. 



The degree of accuracy attainable by this device depends on 

 the care taken to read the scales. In case the reading is cor- 

 rect to \ mm., the result is accurate to one part in a thousand. 



Typical examples of the kinds of equations which can be solved 

 by this graphical method of proportional parts are: 



