Ivi The Alter of cope explained'. 
tions of the micrometer-fcrew, being exprefled in the 
thoufandth parts of an inch, are eafily read as fallows'. 
Oppofite to 20 revolutions, you find the No. 2933, the 
firft fig. 2, is 2 inches, the fecond being 9, ftiews 
9-tenths, and the two laft figures being 33, are 33 
parts of 100, which we have divided each fingle 
10th of an inch into, by means of the micrometer-fcrew; 
therefore the meafiire of 20 revolutions* is equal to 
2 inches 2-tenths, and T V- 6 dreth parts of another tenth. 
Again, if you meafure nine revolutions by the micro¬ 
meter-fcrew in the fame manner, it will be found from 
the firft table to be 1320, which is equal to one inch* 
three tenths, and twenty parts of 100 of another tenth, 
Likewife in the fame table 1, where we have but three 
figures as at five revolutions, which are 733, here the 
firft is feven tenths of an inch, and the two laft 33 parts 
in 100, of another tenth, that is feven tenths and 
-iVodredth parts, and fo of the reft. 
In the column entitled Diameter in the fecond table* 
the numbers are alfo exprefled in thoufandth parts of art 
inch, fo that the two laft figures to the right-hand are 
decimal parts of one tenth of an inch * the third figures 
from the fame hand are tenths, and all the reft are whole 
inches. As all thefe meafures are computed from the 
number of revolutions of the micrometer-fcrew, in pafiing 
over the magnified image of i-ioth of an inch ; it is 
plain, that the numbers in this column which ftand againft 
the number of each magnifier, exprefs the true meafure 
fof the magnified image. 
Example. 
Againft the third magnifier which is fet in a button* 
We find 6951* this fhews that one fingle tenth part of 
