Tetra Die Unerreichbare / Open Case Back

Reference 477 is the sapphire-back version of the NOMOS Tetra Die Unerreichbare, with a 29.5mm square stainless steel case, silvercut-polished dial, rose small seconds sub-dial, rhodium-plated hands, a turquoise seconds hand, and the hand-wound Alpha calibre. It follows the same dial and strap configuration as the closed-back version, with the movement visible through a sapphire crystal case back. The stainless steel case measures 29.5mm by 29.5mm, with a height of 6.5mm and a lug-to-lug length of 40.5mm. It is fixed with four screws and fitted with a sapphire crystal front and sapphire crystal case back. The Tetra case is defined by its square shape, flat profile, and stepped double lugs. Water resistance is rated to 3 atm. The silvercut-polished dial uses the Tetra’s mixed numeral and marker layout, with a square minute track and a contrasting rose small seconds display at 6 o’clock. The turquoise seconds hand adds a separate colour accent within the sub-dial, while the rhodium-plated hour and minute hands keep the main display aligned with the silver-toned dial surface. Power comes from the NOMOS Alpha, a manually wound in-house calibre measuring 10 ½ lignes in diameter and 2.6mm in height. It has 17 jewels and a power reserve of up to 43 hours. The movement is visible through the sapphire crystal case back. The watch is supplied on a velvet gray vegan velour remborde strap with an 18mm lug width.