3H，4H是指铅笔的硬度，就如楼上所说硬度分H和B的，至于3H能达到什么样的防划程度，这是一个概念的问题，首先要确立的是，耐磨和硬度不是一个概念，就象轮胎很耐磨但是不硬，而划伤是硬度与耐磨性的综合表现，不能用几个H来体现的。
1.首先观察洛氏硬度计表表盘指针是否归零，如下图，大指针归零时同时指向红色字母B和黑色字母C，小指针归零时则处于黑色圆点处。
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2.观察工作台、压头是否合适，如果不合适则在选用合适的换上。
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3.如下图所示，选择试验力选择钮为150档位。
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4.观察加力手柄和卸力手柄是否如图中所示。
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https://iknow-pic.cdn.bcebos.com/279759ee3d6d55fb5b11033f61224f4a21a4ddd0"/>
5.将样件平稳地放在工作台上。
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