standard measure of quantity

例句：

1. 1.The standard for measuring the length of a ruler is 20 cm.
   测量尺的标准长度是20厘米。
2. 2. This is the standard way to do it.
   这是做这件事的标准方式。
3. 3.The standards for quality control have been raised.
   质量控制的标准已经提高。