Tell them apart

1.3.4 — the 6 pairs that get mixed up

Most mix-ups happen when two words sit next to each other. These are the 6 pairs worth practicing apart. The 4 marked most confused are the ones the course itself flags, or that sit closest together.

Cover the right-hand column with your hand, read the left definition, and say which term it is out loud before you look. Then swap sides.

most confused
latitude

North-south. Measurable in the 16th century from the sun or Polaris.

vs
longitude

East-west. Needed a clock they did not have. Guessed by dead reckoning.

How to tell Same grid you used in 1.3.2. The new fact is that only half of it was usable at sea.
most confused
primary source

Firsthand: a log, letter, diary, or artifact.

vs
secondary source

A later retelling. This essay.

How to tell If a question asks what you just read, the answer is secondary. The captain's log would have been primary.
most confused
astrolabe

Sun or star height. Essay: mainly on land.

vs
cross-staff

Same kind of measurement at sea. The trusted tool in latitude sailing.

How to tell Do not swap them. Cross-staff is the one the essay says they trusted on the ocean crossing.
most confused
true north

Geographic pole. What maps are drawn on.

vs
magnetic north

Where the compass actually points.

How to tell The gap is magnetic declination. 16th-century compass maps often look slightly twisted because they used magnetic bearings.
dead reckoning

Estimate speed and course, convert to distance, plot it.

vs
parallel sailing

Hold one latitude all the way across with the cross-staff.

How to tell Dead reckoning is the east-west guess. Parallel sailing is how they avoided needing a good east-west guess until they had to measure one straight run.
map

Land surfaces.

vs
chart

Sea coasts.

How to tell The essay's opening split. Same idea, different surface.
If you only remember one thing Demography is the study; demographics are the data. Population is how many; density is how packed. Deviance is society rejecting you; a counterculture is a group rejecting society. Culture shock is the feeling; acculturation is the adjusting.