To observe how the scales are read, click in the "checkbox" by SHOW
and drag the lower scale left or right to observe how the measurement is determined.
Notice that the value for the upper scale is determined by where the 0 on the lower scale lines up with the upper scale and the number on the lower scale is determined by finding which mark on the lower scale best lines up with ANY mark on the upper scale.
To test your ability to read a measurement, leave SHOW unchecked and then drag the lower scale left or right.
The applet will wait for you to enter a value into the TextField and
will then tell you whether your answer is correct.
(After you type in an answer, press Enter.)