Set the micrometer to its baseline by aligning the center line of the cylinder with the zero mark on the thimble.
Measure a pencil. Place the pencil between the measuring rods. Using the friction screw, rotate the thimble around the cylinder, which closes the rods against the pencil. Tighten the rods against the sides of the pencil snugly. Lock the pencil in place using the locking lever.
Look at the intersection of cylinder center line and the thimble markings. The cylinder measurement is the measure to the left of your decimal point in millimeters. The thimble measure is the measurement of the microns to the thousandth of a millimeter.
Estimate the reading on the micrometer. Recall that every mark on the cylinder is half a millimeter. Count the marks. If the thimble rests against the cylinder between markings, you can estimate that the reading you add from the thimble will likely be within 3 micrometers of the actual reading. Add the measurement from the thimble to the cylinder measurement. This will give you the distance between the measuring rods holding the pencil.
Note that the cylinder measures 7 1/2 mm. This is equal to 15 marks on the cylinder. The thimble reading is 0.140. This is equal to the thimble mark intersecting the base center line of the cylinder. Count every mark as one. So four marks after the 10 measure on the thimble is 14. Add the two measures together. The measure between the rods is 7.640 or 7,640 micrometers or microns. Look at your millimeter-to-micrometer chart to verify that 7 mm is equal to 7,000 micrometers to know that your estimate is correct.