视图模型不仅暴露模型，还有属性（比如状态信息，就像“is busy”指示符）和命令。

The viewmodel exposes not only models, but other properties (such as state information, like the "is busy" indicator) and commands

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而且由于每个UNIX命令都返回一个指示成功或失败的状态代码，因此，您可以使用任何命令作为“条件”——而不仅仅是使用测试操作符。

And because every UNIX command returns a status code reflecting success or failure, you can use any command as a conditional — not just the test operators.

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通过计算扭矩命令值和响应于扭矩命令据报告输送的扭矩量之间的差值而获得第二指示符。

A second indicator is obtained by calculating the difference between the value of a torque command and the amount of torque reportedly delivered in response to the torque command.

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