Hover or tap underlined Spanish terms to see their translation and exam tip.
Si el error de índice (Ei) de un sextante es superior a 3' y se desea reducirlo, ¿sobre qué tornillo de ajuste debe actuarse principalmente?If a sextant’s index error (Ei) exceeds 3' and you wish to reduce it, which adjustment screw should mainly be turned?
Show the answer
Correct answer: b) The parallelism adjustment screw of the horizon (small) mirror.
Why it is correct
Index error occurs when the horizon glass and index mirror are not strictly parallel when the index arm is set to 0° 00′. After checking mirror perpendicularity and removing side error, index error is removed by turning the parallelism screw on the back of the horizon (small) mirror.
Why the others are not
- a) That first adjustment makes the index mirror perpendicular to the frame, rather than setting 0° parallelism.
- c) The perpendicularity screw on the horizon glass corrects side error (lateral misalignment).
- d) The telescope collar corrects collimation error (parallelism of the optical axis with the frame).
How to work it out in the exam
- Mechanical adjustment of index error (> 3′): parallelism screw of the horizon (small) mirror.
Where this question comes from
- Ministerio de Transportes (Madrid) · 2026 · Convocatoria de abril · CY Test 1 · question 7 Official paper · Official answer key
- Ministerio de Transportes (Madrid) · 2026 · Convocatoria de abril · CY Test 2 · question 1 Official paper · Official answer key
Pending instructor review. Machine translation, not reviewed.