Which instrument is used when accurate angle settings are required?

• A. The sine bar
• B. A dial indicator
• C. Vernier caliper
• D. Micrometer

Answer: (A)

When you need an exact angle, the sine bar is the tool of choice because it translates a precise vertical height into a precise angle relative to a reference surface. The bar sits on a flat plate with a fixed length between its two reference faces. By stacking gauge blocks to a certain height under one end, you create an angle where sin(angle) equals the height divided by that fixed length. So you can set the exact angle you want by choosing the correct block height, then align the workpiece to match that angle. This method gives repeatable, high-accuracy angle settings.

The other tools measure linear distances or small displacements rather than directly defining an angle. A dial indicator checks how much something deviates from a reference line, while a vernier caliper and a micrometer measure lengths, not angles, so they don’t provide a straightforward route to precise angular settings.