On an unusually warm day in early March, I was invited to visit Sinn headquarters in Frankfurt, Germany. Sinn had prepared a special program including a special exhibition showcasing their technologies over the last 30 years in the main foyer. This was followed by a factory tour, and finally seeing their latest collection. 

Most of us are familiar with the origins of Sinn, which all started with Helmut Sinn, who was a flight instructor, and former World War II pilot. The company’s core business under his ownership was the manufacturing of navigation clocks and pilot chronographs. In 1994, certified engineer Lothar Schmidt acquired the company from Helmut Sinn and renamed it to “Sinn Spezialuhren GmbH”. Lothar Schmidt worked previously with IWC, and was also part of Günter Blümlein’s team to revive A. Lange & Söhne.

This year Sinn is celebrating 30 years since Mr. Schmidt acquired the company. It was a coincidence that the day of my visit, news broke regarding Mr. Schmidt’s succession plans. He will celebrate his 75th birthday this year, and announced plans to create a foundation similar to the Hans Wilsdorf Foundation, that will own the shares of Sinn and its subsidiary companies. Mr. Schmidt also owns the SUG casemaker in the famous watchmaking village of Glashütte. 

Over the past 30 years, Mr. Schmidt, with his engineering background, has developed several technologies for Sinn watches. In 1995, Ar-Dehumidifying Technology was introduced for the first time, which prevents the crystal from fogging up even when faced with sudden temperature changes. In 1996, Mr. Schmidt introduced the Hydro technology that guarantees zero fogging, pressure resistance at every accessible diving depth and optimal readability under water at any angle. In the later years, Tegiment and Diapal technologies were also introduced. I will focus on the Hydro technology in-depth since I spent considerable time with a Sinn engineer specializing in this technology.

Lothar Schmidt

My first stop in the factory tour was the surfacing department. Lars Eller, who is single handedly responsible for this department, stated that he refurbishes cases that are sent as part of servicing, and he is also responsible for bead blasting of the new cases and bracelets. On average he resurfaces 300-400 cases per year. This includes grinding, welding for deep marks on steel, titanium, gold, and even platinum cases. 

All the surface hardened “Tegimented” cases are manufactured by Sinn’s sister company, SUG, in Glashütte. Tegimented cases are bead blasted using ceramic beads after the cases have been through the hardening process. While there are two manual machines for bead blasting in Sinn manufacture, SUG has two automated machines that have the capacity to complete 70 cases in 40 minutes. SUG not only supplies cases to Sinn, but also to several Swiss and German watch companies, including A. Lange & Söhne.

My next stop was the watchmaker’s department. Sinn has 16 watchmakers working in production, and another 16 watchmakers for after sales servicing.  What was unique from my other visits to manufactures was that each watchmaker at Sinn is responsible for the complete assembly of the watch. Usually there is an assembly line where a watchmaker specializes in certain tasks, then the watch moves down the assembly line until it is completed, and quality control is done. However, at Sinn a single watchmaker is responsible for complete assembly of each watch. Sinn believes this method is more efficient and easier for quality assurance.

As for the movements, the majority of the movements Sinn uses are provided by Sellita and Concepto movement makers. They are regulated for +3 to +10 seconds tolerance per day, and with an amplitude range between 280-330 degrees. Each movement is measured in four positions – dial up, dial down, crown up, crown down. 

After the watchmaker’s department, I visited a few different technology departments, but I spent the most time learning about Sinn’s Hydro technology. Mr. Nolting, the head engineer, explained that Hydro technology was developed as part of a requirement from German Naval Special Forces Command, also called the Kampfschwimmer (KSM). KSM issued a public tender with requirements that  a watch have the best visibility and robustness underwater. Sinn won that tender and the UX watch was selected as the official watch of KSM. 

The issued UX S KSM is obviously not available to the public. However, it is almost identical to the civilian version of the watch, sharing the same case made of hardened submarine steel and coated with a scratch-resistant ceramic layer. And the UX S is essentially the same as the UX S GSG9, another variant of the watch made for GSG 9, the counter-terrorism unit of Germany’s federal police.

So, how does Hydro technology work? The quartz movement, dial and hands are immersed directly in a crystal-clear silicone oil. The watch is thus free from fogging, as there is no air inside the case. The clear oil has the same refractive index as that of the sapphire crystal glass. As a result, light continues to penetrate through the sapphire crystal even from a wide angle of observation. Therefore, a Hydro watch can be read from any angle underwater. According to Mr. Nolting, the proprietary clear oil that Sinn uses does not have a patent, however, the company keeps their formula as a guarded secret. He said many have tried to replicate it, but none have succeeded so far.

The Sinn proprietary oil is incompressible. It replaces the air inside the case which inevitably contains moisture. When there is no air humidity, there can be no condensation. Hence, the diver will see zero fogging and perfect visibility from any angle. The crystal is 3.5mm thick and Hydro watches are 5,000 meters water resistant. The caseback is also special – it has a membrane to prevent the crystal from exploding under pressure. Because the oil used changes volume by 10% between the temperatures of −20 °C to 60 °C, the case needs to be flexible. Sinn installed a membrane caseback that compresses and expands in accordance with the oil within the watch, preventing the crystal from exploding.

Sinn’s temperature resistance technology, tested

Sinn uses ETA quartz movement in UX series and Ronda quartz in U50 Hydro watch. The movement is set inside a vacuum capsule. A special 3V lithium-ion battery is used to power the movement which Sinn guarantees for 5 years. The battery replacement requires the watch to be sent back to Sinn manufacture and it takes 4-6 weeks for change of the battery. This requires removal of the oil, dissembling the movement, filling back of the oil, and 24 hours for testing. It costs 275 euros for the replacement of the battery. Mr. Nolting states that they usually replace the entire quartz movement just to ensure proper operation and refilling the oil.

A Sinn undergoing a pressure test

Lothar Schmidt’s Sinn, in my opinion, has been an engineering company first, and watchmaking second. At some point we have all said that Sinn watches can be over-engineered, but this is a compliment for a CEO who is an engineering perfectionist. He takes pride in designing solutions like Hydro technology when he receives a challenge of building a distortion-free watch for a highly specialized use case. Sinn

All photos furnished by Sinn