STANDARD PLANIMETER. 79 



B, to follow the entire outline freely. If the area to 

 be determined is too large to permit placing the sta- 

 tionary pin outside, and thus determining the area as 

 a whole, the area may be divided and its parts deter- 

 mined separately. 



(2) Place the tracing pin at any starting point on the 

 outline of the area and press it in to make a distinct 

 mark on the surface. Set all the scales at zero with 

 the hand. Then draw the tracing pin around the out- 

 line of the area, following it as exactly as possible, until 

 the circuit is completed and the tracing pin rests at the 

 starting point. The circuit must be made in the same 

 direction that the hands of a watch move. 



(3) Four figures, representing tens, units, tenths, and 

 hundredths, may be read after the circuit is completed, 

 and the reading may be from 00.01 to 99.99. Figure 

 12 shows a sample reading of 25.71 square inches 

 because the dial C registers 10 square inches for each 

 numbered division. The roller D registers 1 square 

 inch for each numbered division. The vernier E regis- 

 ters 0.01 square inch to be read against D. 



It will be noted that the pointer at dial C points 

 between 2 and 3. The area in square inches is, there- 

 fore, between 20 and 30. The zero on the vernier E 

 serves as a pointer for the roller D. This reads be- 

 tween 5 and 6. Therefore the integral area is 25. 

 Counting the divisions between the figures 5 and 6, it 

 is seen that the zero on the vernier barely passes the 

 seventh mark. Therefore the first decimal is 0.7. By 

 looking along the vernier E it will be seen that one of 

 the graduations falls exactly opposite one of those on 



