At first, let me quote some dialogues from Pirates of the Caribbean $5$: Dead Men Tell No Tales.

enter image description here In a scene when she wants to purchase a chronometer, she has accused that she is a witch, but she defends herself in this way: "No, I'm not. Am I a witch for having cataloged over 200 stars?"

Also in another scene when she accused to be a witch, she defends herself in this way "I'm an astronomer."

enter image description here In a scene in the ship on the sea, Carina says:

"This chronometer keeps the exact time in London.
I'm using it to make an altitude measurement to determine longitude.
Only then will we find our exact spot at sea.

Following this scene, she says: "I'm not only an astronomer, I'm also a horologist."

so we can conclude that:

she is an astronomer and a horologist with facilities and possibilities of only a chronometer and a pen and a book(or notebook), and an astronomical table in that book or in her mind, with no other additional equipments.

But Captain Jack's crew look at her like fools! It seems that I am on the same side as Jack's fool crews! Also, the film emphasizes that Carina is a woman of science and an astronomer, and I believe that there is a scientific support behind this dialogue.

How did she measure the altitude and determine the longitude by use of the chronometer?


A sextant can be used to measure the altitude (angle above the horizon) of the sun in daytime or a known bright star at night. This altitude (together with a set of astronomical tables called an ephemeris) can be used to calculate local time. If you also know the current time in London from an accurate chronometer (clock) then you subtract one time from the other and multiply by 15 degrees per hour difference to find your longitude.


I think you are interested in Marine chronometer invented by John Harrison,
also, one can find this video helpful.

  • $\begingroup$ I didn't see the film! $\endgroup$ – cgiovanardi May 17 '18 at 11:19

Following this video from the answer by @cgiovanardi, I have faced too many related videos on youtube, and finally, $\color{Green}{\text{I have found this short}}$ video $\color{Green}{\text{, which answer the question!}}$

Also, the following videos explain how to use your watch as a compass i.e. how to find North using a wristwatch: video_1, video_2, video_3, video_4.


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