Sextant

Question 1

What is a sextant used for?

Answer 1

Vertical sextant angle
Horizontal sextant angle
Celestial navigation

Question 2

What permanent errors are there? Sextant

Answer 2

Graduation error
Collimation error
Centring error
Shade error
Worm- & rack-error

Question 3

What Adjustable errors are there? Sextant

Answer 3

PSI

Perpendicular error
Side error
Index error

Question 4

What is Perpendicular error?

Answer 4

Index mirror is not perpendicular to the plane of the instrument.

To check turn the sextant round, hold it horizontal and look into the index mirror.

If the true and reflected areas do not line up then the error exists.

To adjust for this error turn the screw at the top of the mirror

Question 5

What is Side error?

Answer 5

horizon mirror is not perpendicular with the plane of the instrument.

To check for this, set the arc to zero, hold the sextant on the side and look through the telescope at the distant horizon.

If true and reflected horizons do not line up, then side error exists.

To correct, slowly tighten or loosen the the screw furthest from the frame at the back of the horizon mirror until the vertical line no longer appears to jump

Question 6

What is Index error?

Answer 6

index and horizon mirrors are not parallel with each other when the arc is set to zero.

To check for this error, set the arc to zero, hold the sextant vertical and look at the distant horizon.

If the true and reflected horizons do not line up, index error exists.

To correct, turn the screw at the top of the mirror and then re-check for side error and again for index error