On a certain day, the highest temperature during the day is +2°C, and the lowest temperature at night is -9°C, what is the temperature difference between day and night in °C?
某天白天最高气温是+2°C，晚上最低气温是-9°C，这天昼夜温度相差多少°C．
<gadget id="calculator">2 + 9</gadget>
<output>11</output>

<result>11</result>