Six in the Morning on the Izu Peninsula
It was six in the morning in Osezaki bay, on Japan's Izu Peninsula. The surface of the water was still windless and looked six degrees colder than it was. As the diving instructor Kenji Arata checked his equipment, the guest who had just arrived was still drinking tea from her flask: Dr. Naomi Iwase, who works on oscillators in a metrology laboratory in Tokyo.
Naomi looked at the watch on Kenji's wrist: "That is new. You were not wearing it yesterday."
"Yesterday I was diving with a diver's watch," said Kenji, laughing. "Today I am diving with a chronometer. The Grand Seiko Spring Drive U.F.A. Ushio 300. This is the green dial, the SLGB025; there is a blue dial too, the SLGB023."
"You are not the first person to use the word chronometer for a diver's watch," said Naomi, "but usually they exaggerate. What is the accuracy of this one?"
Kenji held out his arm: "Plus or minus twenty seconds a year."
Naomi lowered her flask: "A year? You meant a month, surely."
U.F.A: What Twenty Seconds a Year Means
"A year," Kenji repeated. "That is what the letters U.F.A. are for: Ultra Fine Accuracy. Grand Seiko gives that name only to Spring Drive calibres that hold the limit of plus or minus twenty seconds a year. This watch has the 9RB1."
Naomi did the arithmetic for a moment: "Twenty seconds divided by twelve months is about one point seven seconds a month. In other words a monthly deviation better than the daily deviation of an average mechanical watch. So how do they do it? The heart of a Spring Drive is a mainspring, but its reference is quartz."
"Exactly so," said Kenji. "The energy comes from the mainspring, which means there is no battery. But the speed the spring is allowed to release is policed by a quartz oscillator. The system brakes not the hand but the wheel itself. That is why the seconds hand does not tick, it glides."
"And that," said Naomi, "is why the limit of the accuracy is not in the spring but in the quartz. The frequency of quartz drifts with temperature; in the laboratory we call that its temperature coefficient. To get down to twenty seconds a year you have to select the crystal, age it, and measure its thermal behaviour one piece at a time. That is not a design job, it is a sorting job."
Kenji nodded: "Which is exactly what Grand Seiko does. Every U.F.A. calibre is measured and regulated individually. And there is a diving side to this, Naomi: my job is to keep people under water. If you measure bottom time wrongly, you calculate the decompression stop wrongly too. For a diver, accuracy is not a boast, it is a line in the safety budget."
format_quote"For a diver, accuracy is not a boast, it is a line in the safety budget."
Kenji Arata, diving instructor
Forty Point Eight Millimetres: The Engineering of Getting Smaller
Naomi looked at the watch from the side: "It looks slimmer than I expect from a diver."
"This is the smallest diver Grand Seiko has made," said Kenji. "Forty point eight millimetres across, twelve point nine high. The material is high intensity titanium: roughly half the weight of steel yet a harder alloy. It is water resistant to three hundred metres, it has a screw down crown, and the clasp extends to go over a wetsuit."
"It is the Evolution 9 line," he added. "Which means the dial and the hands have been recalculated for legibility. Light halves every ten metres under water. The dial is called Ushio, the tidal current; the green one is close to the morning colour of this bay, the blue one to its midday colour."
Naomi touched the flank of the case: "And there is this: making something smaller is the hardest engineering task there is. Holding the same pressure rating in a smaller volume does not happen without paying for it in wall thickness and case geometry."
"Which is what the titanium is for," said Kenji. "Thicker walls, a smaller weight penalty."
At the Geneva Table
Before putting on her mask, Naomi asked: "Has this watch gone to Geneva?"
"In the sports category," said Kenji. "One hundred and ninety four brands entered three hundred and twenty watches in this year's competition. The shortlist is announced at the beginning of September and the prizes are given in November."
"If there were a metrologist on that jury," said Naomi, laughing, "they would look at a single line in this watch's file: plus or minus twenty seconds a year. Because that number is not a claim, it is the result of a measurement."
Kenji put the regulator in his mouth and went into the water. The green dial was still green through the first metres; at five it turned blue, at ten it turned grey. What it was measuring never changed at all.
format_quote"That number is not a claim, it is the result of a measurement."
Dr. Naomi Iwase
