When the little sloppy uses a protractor to measure an angle, he mistook the scale on the outer circle for the scale on the inner circle and read 150 degrees. What should be the correct reading?
小马虎用量角器测量一个角时，由于误把外圈刻度当成内圈刻度而读得度数为150度，正确读数应该是多少．
<gadget id="calculator">180 - 150</gadget>
<output>30</output>

<result>30</result>