Ming East India Company

Later sextants were all made of metal. The arc-shaped reading surface of the sextant was polished and ground, making it extremely smooth and easy to slide.

However, this wooden product is too rough. The contact surface between the indicator arm and the scale arc is as if it is covered with glue, and it cannot be pulled evenly no matter how hard you pull it...

Not to mention calibration and fine-tuning.

Afterwards, Shirano had people continuously improve the polishing of the wooden contact surfaces, but wooden products are not as easy to process as metal products. Even after the craftsmen polished the contact surfaces to a shine, they still couldn't make them usable...

"Master, I dare to offer a word."

Seeing Bai Ye sweating profusely with anxiety, Su Zhongman, who had been by Bai Ye's side, stepped forward:

"Master, why don't you paint this wooden frame with some oil? Ryukyu has built so many large ships over the years, there's plenty of tung oil."

Shirono's eyes lit up. Although there was no special lubricant in this era, parts such as carriage axles did have a need for lubrication, so using tung oil for lubrication was indeed a good idea.

Shirono carefully applied tung oil to the entire surface, and sure enough, the indicator arm, which had been stiff just moments before, could now be dragged very easily.

The only drawback is that tung oil dries very easily, and with repeated use, a thick layer of oil will accumulate, obscuring the readings.

Shirano could only provide the sextant with a bottle of tung oil and an oil scraper. Before each use, he would apply a layer of tung oil, and then scrape off the oil layer periodically over time.

Having solved the lubrication problem, the second problem arose: precision.

Since there were no specialized CNC machine tools, in order to divide a one-sixth circle into 120 equal parts, the only way in this era was through the carpenter's own intuition.

However, the arc length corresponding to 1 degree on a sextant is only a few tenths of a millimeter, and purely handmade products will definitely have huge errors.

Modern sextants require an accuracy of at least the second level, which is approximately 1/360th of a degree. Even with this accuracy, there is still some margin of error in practical use, so the quality of these handmade gadgets is even more questionable.

"Master, this is the thirtieth sample that has been discarded." Su Zhongman said cautiously.

Bai Ye kept sending people to rework the samples, but what frustrated him was that dozens of samples in a row did not match the latitude and longitude he remembered.

Extremely frustrated, Shiro once again resorted to the robot swarm tactic, relying on continuous trial and error to assemble the most suitable one.

At Shirano's command, the island's craftsmen stopped all ship repairs and manufacturing, and devoted themselves to grinding and forging the sextant.

Shirane requisitioned almost all the glass products on the island and sent people to import even more glass from Ming China and Japan.

Hundreds and thousands of sextants were manufactured, and Shirano compared them one by one.

Ryukyu has countless islands, with a latitude difference of about 3 degrees from Hateruma at the southernmost tip of the islands to Iwo Jima at the northernmost tip.

Before crossing over, Shirayuki was a senior member of a sailing club, so he must have memorized the specific latitude and longitude of Ryukyu and the various islands in the East countless times, and the relevant coordinates were already engraved in his mind.

Furthermore, Hakuno established a tight control over islands such as Amami, Miyako, and Yaeyama.

Now, Shirano can confidently navigate his own boat between the islands to calibrate the degree differences.

Soon, the people of Ryukyu and the surrounding islands witnessed a strange sight: in the months following the initial conquest of Ryukyu, Shirano, as the de facto supreme ruler of Ryukyu, basically did not spend more than a few days on the island.

Instead, he frequently sailed around the sea in the Ryukyu naval vessels he had captured.

Then, instead of fishing or robbing, he just sat there every night looking at the stars with a bunch of "toys"...

"This looks like it would be suitable."

After eliminating countless unfinished products, Shirano finally selected what he considered to be "qualified" products.

After he continuously adjusted the verticality of the arc arm and calibrated the sextant's degrees, the wooden sextant matched the latitude and longitude coordinates he remembered.

Shirono named his work "Ark No. 1" as the standard machine for making sextants in the future.

With the standard machine in place, the rest was simple. Subsequent craftsmen only needed to follow the example and ensure that the readings they produced were as consistent as possible with those of Ark 1.

Even with some errors, the new sextant can be calibrated by measuring the latitude at the same location as Ark-1.

With this thing, Bai Ye can completely throw Cheng Keqin's overseas star-gazing technique and needle path manual into the trash can. He can now mass-produce ship captains anytime, anywhere.

To maintain his monopoly, Shirane ordered that the sextant prototype be kept strictly secret, and that its operation be mastered only by people whom Shirane considered "absolutely reliable." Furthermore, the calibration had to be carried out by members of the Shirane clan.

As for the crucial prototype, "Ark One," Shirano even built a special storage room in Shuri Castle, which was personally managed by his father, Shirano Fumimaro.

In the era before patent rights, Shirayuki could only establish technological barriers by adopting the feudal system of "passing down to sons but not daughters, and to family members but not outsiders".

The problem of measuring longitude has been solved for the time being, but for Baiye, simply knowing the latitude is obviously not enough.

The shipping routes from the Ming Dynasty to Ryukyu or the Eastern Ocean were relatively short because the land route followed the direction of the Kuroshio Current. As long as you followed the ocean current and used the islands as coordinates, you could eventually drift to the Eastern Ocean unless you were extremely unlucky. Therefore, the requirement for longitude was not very high.

However, for ultra-long-distance trade spanning the Pacific and Indian Oceans, simply identifying latitude is not enough.

Especially for sailing navies, which often deviate from their course to make large-scale maneuvers and raids at sea, the risk of running aground and sinking is extremely high if the measurement accuracy is not good.

Even more than a hundred years later, the British Royal Navy still managed to pull off a blunder by heading straight for Portsmouth but ending up at the Isles of Scilly, which are at the same latitude but more than 300 kilometers away.

Longitude measurement is essentially a time measurement. The Earth rotates from west to east, and by measuring the time difference between two places and dividing it by a day of 24 hours, we can know the difference in longitude between the two places.

Measuring local time is easy; there are gnomons and sundials on Ryukyu Island.

If all else fails, the most primitive calculation method can be used: the shortest time of day is 12 noon, and then an hourglass or clepsydra can be used to assist in timing to obtain the specific time.

However, accurately measuring the time a ship spends at sea is extremely difficult.

Two centuries before the invention of the modern marine chronometer, Shirano believed it was impossible for him to master all the prerequisite technologies for the marine chronometer in a short period of time.

Therefore, we can only settle for second best and use a method that was once eliminated in the longitude measurement war—the lunar distance method.