Log on to an interactive micrometer website, such as the one used in the Durham University Physics lab (see Resources). Click the "test" button to use the interactive controls. Unlock the measuring lock by clicking the lock lever at the right of the calipers.
Press the up arrow key to rotate the thimble and open the calipers. Use the down arrow key to close them. Place the mouse pointer between the calipers on the screen with the left side against the left caliper. Use the arrow keys to close the caliper jaws around the cursor and measure its thickness.
Read the half millimeter marks on the coarse scale. The coarse scale is on the rod that's even with the caliper jaws. Its measurements are revealed as the thimble rotates to open the calipers. Each hash mark above the horizontal line represents one millimeter, and the marks below the line show half millimeter measurements. The coarse scale should show around two millimeters, depending on your cursor.
Read the thimble scale to find the fine measurement in tenths and hundredths of millimeters. The thimble notates a number at every 5/10ths millimeter. Look at the two thimble marks closest to the horizontal line on the coarse scale. Estimate the location of the horizontal line between the thimble lines on a scale of 1 to 10. For instance, if the horizontal line on the coarse scale is between the 5/10ths and 6/10ths marks but much closer to the 6 line, then the fine measurement would be roughly .58 millimeters.
Add the coarse measurement to the fine measurement for the total thickness of the object measured. The mouse cursor in consideration for this example had a coarse measurement of 2 millimeters, and a fine measurement of .58 millimeters, for a total thickness of 2.58 millimeters on the interactive micrometer.