12 
PHARMACEUTICAL BOTANY 
4. Note the known value for each division of the stage micrometer 
scale which may either be etched on the stage micrometer or indi- 
cated on a label found pasted upon it. If the value indicated is 0.01 
mm. (/"loo mm.) then each division of the stage micrometer scale 
has a value of 10 microns; if 0.1 mm. (}^o mm.), 100 microns. 
5. Multiply the number of included divisions of the stage microm- 
eter scale by the value in microns given for each division and divide 
the result by the number of included divisions of the ocular microm- 
eter scale. The quotient represents the value of each division of 
the ocular micrometer scale. 
6. Note the optical combination (number of ocular, objective and 
tube length) used and keep a record of it with the calculated microm- 
eter value. Repeat for each of the combinations. 
To measure an object by this method read off the number of 
divisions it occupies of the ocular micrometer scale, and express the 
result in microns by looking up the recorded value for the optical 
combination used. 
