Prismatic Compass Sight Vane Components

The sight vane of a Prismatic Compass is the assembly used for taking readings. Its primary function is to allow the user to sight a distant object while simultaneously viewing the compass card.

Components of the Sight Vane Assembly

The typical components that form the sight vane assembly on a Prismatic Compass include:

• Sighting Vane: A metal strip, often with a vertical hair or line, used to align with the object being sighted.
• Prism/Eyepiece: Allows the user to view the compass card and the object line simultaneously.
• Mirror/Reflector: Used to reflect the image of the compass card towards the prism/eyepiece.
• Frame: The structure holding these components together.

Analysis of Options

Let's analyze why each option relates to the Prismatic Compass:

• Mirror: This is a crucial part of the sight vane assembly, reflecting the compass card.
• Object vane: This is the object or point in the distance that the user sights. It is the target, not a component *of* the sight vane itself.
• Pivot pin: This pin supports the compass needle, allowing it to rotate freely. It is central to the compass mechanism but is not part of the sight vane assembly used for observation.
• Sliding frame: This typically refers to the frame that holds the sighting vane, prism, and mirror. It is functionally part of the sight vane assembly.

Conclusion

The pivot pin is essential for the compass needle's rotation but is mechanically separate from the sight vane assembly. While the object vane is also not part of the sight vane, the pivot pin is a core compass component distinct from the sighting mechanism itself. Therefore, the pivot pin is not a component of the sight vane.