If you think of the lines on the Sleeve as dollars and quarters, the
lines on the Thimble represent "pennies" or cents.

As the thimble rotates, you add those pennies to the dollars and quarters

O.K. so now we know how to read a micrometer! We just need some
practice. In the picture below, the Sleeve shows 3 dollars and one
quarter (25 cents). The Thimble shows one penny. To calculate
this reading we add 3 dollars plus 1 quarter plus 1 penny. The actual
measurement is .326 inches.