Concept quiz

Twelve questions on the ideas people most often get wrong. No tables, no arithmetic. Take it before you start and again when you finish: the first and latest results are kept on this device and compared.

1 Why is one minute of latitude one nautical mile?The nautical mile is defined as one minute of latitudeIt is a coincidence of the size of the EarthIt is only true at the equator

2 At latitude 60° N, how long is one minute of longitude?One nautical mile, the same as everywhereHalf a nautical mileTwo nautical miles

3 The almanac gives the Sun’s GHA and declination for…Your ship’s zone timeUniversal Time (UT), the time at GreenwichLocal time on your own meridian

4 Your watch is 8 seconds fast and you forget to correct it. Your fix moves…Not at all: seconds do not matterAbout 8 miles north or southAbout 2′ of longitude east or west

5 The Sun’s GHA is 100°. Its ground position is at longitude…100° W100° E80° E

6 The index error is 2.0′ on the arc. The index correction is…+2.0′−2.0′Nothing: index error only matters for stars

7 The dip correction for height of eye is…Always subtractedAlways addedAdded for the Sun, subtracted for stars

8 For a noon latitude, you take the Sun’s altitude…At 12:00 by your watchAt its highest, as it crosses your meridianAt sunrise and sunset, and average them

9 One altitude of one body tells you that you are…At one pointSomewhere on a circle around the body’s ground positionOn your DR’s latitude

10 Ho is greater than Hc. You lay off the intercept…Toward the bodyAway from the bodyToward in the north, away in the south

11 The assumed position is…Your best estimate of where the boat isA convenient point near your DR that makes the table entries whole degreesThe body’s ground position

12 Three star lines make a very small triangle (cocked hat). This means…The fix is certainly accurate to the size of the triangleOne of the sights must be wrongThe lines agree, but an error common to all of them (in time or dip, say) can still move the whole triangle