double protractor

例句：

1. 1. The double protractor is used to measure the angle between two lines.
   双角规用于测量两条线之间的夹角。
2. 2. The engineer used the double protractor to check the accuracy of the measurements.
   工程师使用双角规来检查测量的准确性。
3. 3. The double protractor was essential for the construction of the bridge.
   双角规对于桥梁的建设至关重要。