The wall clock in Professor Li's laboratory strikes the hour every hour, and it rings several times. This morning, when he started the experiment, the wall clock chimed the time. When he finished the experiment, the wall clock happened to strike the time again. From the beginning to the end of the experiment, the wall clock rang 33 times. How many hours did Professor Zhang's experiment last?
李教授实验室里的挂钟逢整点报时，几点就敲响几下．今天上午，他开始做实验时，挂钟报时．他做完实验时，恰好挂钟又报时．从实验开始到结束，挂钟一共敲响33下．张教授的实验做了几小时？
<gadget id="calculator">12 - 10</gadget>
<output>2</output>

<result>2</result>