Measure an angle, one side of the angle faces the "180" scale on the protractor, and the other side faces the "120" scale, what is the angle in degrees?
度量一个角，角的一条边对着量角器上"180"的刻度，另一条边对着"120"的刻度，这个角是多少度．
<gadget id="calculator">180 - 120</gadget>
<output>60</output>

<result>60</result>