🔍 Key Concepts

• Side error on a sextant is corrected by adjusting how the horizon glass is aligned relative to either the index mirror or the frame • Know the difference between index error and side error and which part of the sextant each one involves • Visualize what you see in the telescope when correcting side error: the direct horizon and the reflected horizon should line up vertically

💭 Think About

• Which error involves the horizon and index mirrors no longer being exactly in the same plane, causing a vertical separation of the images? • For side error, what must be true about the relationship between the horizon glass and the index mirror when the index is at zero? • Look at each option: which ones describe a condition of being parallel versus perpendicular, and which relationship is actually used to remove side error rather than index error?

✅ Before You Answer

• Identify which adjustment is normally associated with index error (this one you should eliminate for side error questions) • Check which answer specifically references the horizon glass and its alignment to either the index mirror or the sextant frame • Make sure the condition mentions the index set at zero only if that is appropriate for correcting side error, not for another type of error