🔍 Key Concepts

• Differentiate between adjustable sextant errors (user can remove by adjustment) and nonadjustable errors (must be allowed for mentally or by correction tables). • Understand what prismatic, centering, and graduation errors actually are in a sextant. • Think about which errors are due to manufacturing/optical imperfections versus those due to mirror alignment that the navigator can set right.

💭 Think About

• For each listed error, ask yourself: can a navigator remove this error in the field by adjusting mirrors or index arm, or is it built into the instrument? • Which of these errors would typically remain the same over time unless the instrument is re‑manufactured or professionally re‑engraved? • If one of these errors is due to the scale itself or to how parts are physically made, would that be something you can fix with routine sextant adjustments?

✅ Before You Answer

• Be clear on which errors are normally corrected by the standard index error and perpendicularity/side error adjustments. • Identify which of the listed errors is associated with the graduated arc or mechanical construction of the sextant rather than its alignment. • Before choosing “All of the above”, confirm that every single error in the list really cannot be adjusted by the user. If even one is adjustable, that answer cannot be correct.