420 Notes. 



measurement to make the divisions of the scale E, and the neces- 

 sary length of the radius of the circle on which the divisions must 

 be read is given as follows. 



It is assumed that 1 division of -fa inch represents -rwofido °f 

 an inch, therefore 



*=10* . . . . (3) 



Therefore from (2) and (3) 



E = £ A = 10 5 A 



This shows the radius of curvature that is required in 

 making the instrument, and a series of parallel lines ruled on 

 the scale parallel to the base line, ^ °f an i ncn a P ar t, complete 

 its graduation. 



