106 VERNIER CALIPER, 



of the vernier divisions is one-thousandth of an inch less 

 than one of the smallest divisions on the parent scale. 

 Now, if the accompanying figure be examined, it will be 

 seen that the zero of the vernier scale is at a point on the 

 main scale distant rather more than two-tenths of an inch 

 from the zero of this scale ; so that the reading begins 

 with a decimal point, and is followed by the figure 2, 

 representing the two-tenths of an inch, or it reads 0'2 in. 

 Then, following the two-tenths, are three of the smallest 

 divisions or fortieths, so that the reading so far is 0'275 in ; 

 each of the fortieths being equivalent to 0'025 of an inch, 

 and as there are three of these, they are represented 

 by O'OTo in. The vernier zero is half-way to the last 

 fortieth, or nearly so, and several more thousandths will 

 have to be added to the existing figures. The zero is twelve- 

 thousandths on, and the figures to be added are 0'012, 

 giving a total reading 0'287. The number of thousandths 

 to be added after reading the fortieths is found by 

 noting the division line on the vernier scale, which 

 coincides with a division on the parent scale, and 

 taking that reading on the vernier. Thus, for the 

 case in question it will be seen that division 12 on 

 the vernier exactly coincides with one of the parent 

 divisions, and each vernier division being one-thousandth of 

 an inch less than each division on the main scale, the meaning 

 is that the zero of the vernier has moved twelve-thousandths 

 beyond the last division. The whole process of measur- 

 ing the outside dimensions is as follows : First, the 

 screws are loosened and the sliding jaw moved up 

 until the object is roughed gripped ; then the separate 

 sliding piece is fixed by means of its set-screw, and 

 the sliding jaw exactly adjusted until both jaws touch 

 the object without either gripping it tightly or allowing it 

 to feel loose. This is done by means of the adjusting screw. 

 The reading is now taken, the order of doing this being, 

 first the inches, then the tenths, next the fortieths or twenty- 

 five-thousandths, and lastly the remaining thousandths, 

 which must be added on. 



When inside measurements have to be made with a 

 vernier caliper, the projecting portions at the ends of the 

 jaws are used, and allowance must be made for the combined 

 thickness of these when they are close together. This 

 thickness is always given by the makers of the instrument 

 and generally amounts to about 0'250 or - 300 of an inch. 



Another most useful instrument, especially for small 



