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Yachtmaster Ocean revision module 3 of 10

SEXT

Sextant Use and Corrections

Taking an altitude, index error, dip, refraction, semi-diameter, and observation discipline.

sextantaltitude

3 guided lessons · 8 practice questions · 8 flashcards

3 outcomes · self-guided revision
  • Explain taking an altitude, index error, dip, refraction, semi-diameter, and observation discipline.
  • Apply sextant to a realistic onboard situation.
  • Recall the core check: identify the body before reducing the sight.

A self-guided revision companion that explains essential concepts, then helps you practise and test them. It supports—but does not replace—recognised instruction, practical training, assessment or certification. Access is a one-time payment, not a subscription.

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Lesson routeTaking a Useful Sight0/1 read

Lesson 1 of 1

Taking a Useful Sight

A sextant sight is a measured altitude at a precise time. The best mathematical reduction cannot rescue a careless observation. A good routine includes instrument check, horizon selection, body identification, rocking the sextant, time call, and immediate note-taking.

At sea, yacht motion is the challenge. Take several sights when possible, reject obvious outliers, and use a sensible average or best observation according to the exercise and conditions.

  • Identify the body before reducing the sight.
  • Rock the sextant to find the lowest point of the arc.
  • Record time and sextant altitude immediately.
  • Take enough observations to spot outliers.
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