What device is specifically used for precision measuring of angles?

The sine bar is a specialized tool used for precision measuring of angles, particularly in machining and mechanical setups. It consists of a flat bar with two perfectly rolled cylinders (or "pins") at either end, which are set apart a specific distance. By placing the sine bar on a surface plate and adjusting the angle using gauge blocks, you can achieve highly accurate angular measurements. This is especially useful for setting up workpieces at specific angles for machining operations, as the design of the sine bar allows for calculations of sine values that correspond to the distance between the pins and the height of the blocks used to elevate the bar.

While protractors are commonly used for measuring angles, they lack the precision needed for intricate machining tasks, making them less suitable for high-accuracy applications. Similarly, calipers and micrometers are primarily designed for measuring lengths and dimensions rather than angles. Therefore, the sine bar is the most appropriate device for achieving precise angle measurements in a machining context.