The first preliminary talks on the construction and development of the wristwatch were with Dr. Bernd Anders, the then DGzRS managing director. We then made an initial suggestion: a robust timepiece with a GMT function seemed to be appropriate for the “seafaring” purpose. After all, seafaring sounds like endless expanses and crossing time zone borders. The sea rescuers’ feedback on the first suggestion was rather subdued. They wanted the dial and functionality to be reduced to the essentials. Due to the operation close to the coast, for example, the display of a second time zone could be dispensed with.
Watchmaking know-how paired with seafaring competence ultimately resulted in a watch made for extremes: A 4 mm thick sapphire glass defies all water pressure and, above all, harder impacts. A magnifying glass inserted from the inside enlarges the date for easy reading. This was developed by Hans-Jürgen Mühle himself. Before taking over the family business in 1970, he had studied precision mechanics and optics in Jena and was thus able to calculate a distortion-free magnifying glass. This does not have to be placed on the glass from the outside, which means that it cannot be knocked off the flat sapphire glass.
The housing, designed for a pressure resistance of 100 bar, was subjected to a pressure of 250 bar as a test during the development phase. Only when the pressure was increased two and a half times did the bottom of the case give way and was dented spherically. The 4 millimeter thick sapphire glass and the watch as a whole remained waterproof.