所以，如果你需要用数学式子计算一个值，那就只有用表达式返回这个值，没有其他语法结构可用，因为否则就无法处理这个值。
And so while you needed expressions for math to work, there was no point in making anything else return a value, because there could not be anything waiting for it.
如果某个行是分层结构中的叶子节点，则返回的值为1，否则返回值为0 。
The value of 1 is returned if the row is a leaf in the hierarchy, otherwise a value of 0 is returned.
如果你的模型是一个连接在两边的细线的结构，你可以去稍微薄到0.8毫米，否则我们建议至少1毫米的厚度。
If your feature is a thin wire connected on both sides, you can go slightly thinner to 0.8 mm, otherwise we recommend at least 1 mm thickness.
如果你的模型比较小的或你的模型是一个连接在两边的细线的结构，你可以去稍微薄到1毫米，否则我们建议至少3毫米的厚度。
If your model is smaller or your feature is a thin wire connected on both sides, you can go slightly thinner to 1 mm, otherwise we recommend at least 3 mm thickness.
如果你的模型比较小的或你的模型是一个连接在两边的细线的结构，你可以去稍微薄到1毫米，否则我们建议至少3毫米的厚度。
If your model is smaller or your feature is a thin wire connected on both sides, you can go slightly thinner to 1 mm, otherwise we recommend at least 3 mm thickness.
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