Otsuka Lotec No.7.5 Jumping Hour Automatic Watch by Jiro Katayama, Disc Display, 40 mm, Unused Full Set

Jiro Katayama's No.7.5 abandons the conventional dial for an instrument panel of three mechanical ports: a jumping hour aperture, a rotating minute disc and a seconds disc magnified by a sapphire fisheye lens. This example is new and unused, with box, documents, strap and tags.

The Piece

Designed in Tokyo by Jiro Katayama, the Otsuka Lotec No.7.5 is one of the most visually distinctive mechanical watches of Japan's modern independent movement. Time is read through a three-window interface rather than hands: the hour numeral jumps instantly at the start of each hour, a rotating disc replaces the minute hand, and a small seconds disc keeps the dial in constant motion. The arrangement evokes the analog gauges of laboratory equipment and aviation instruments, a miniature mechanical console rather than a classical watch face.

The seconds display sits beneath a sapphire fisheye lens whose optical distortion adds depth and curiosity. Mechanically the watch pairs the Miyota 82S5 automatic, a durable and serviceable Japanese caliber, with Otsuka Lotec's own jumping hour module, which converts conventional hour and minute motion into the disc-based display while keeping dependable reliability.

The 316L stainless steel case carries the same industrial philosophy, finished with hairline brushing and sandblasting instead of mirror polish for a utilitarian, tool-instrument appearance. Katayama began building watch cases and mechanical displays in his small workshop around 2008; early prototypes evolved into the numbered system used today, and the brand gained international recognition when the No.6 won the GPHG Challenge Watch Prize.

The No.7.5 belongs to the modern catalog era, in which Katayama refined modular mechanical displays built on industrial design principles, and it is one of the clearest expressions of that philosophy. Production volumes are extremely limited, which draws independent-watch enthusiasts, mechanical-display collectors, industrial-design enthusiasts and specialists in Japanese horology.

Details

• Maker: Otsuka Lotec (Jiro Katayama, Tokyo)
• Model: No.7.5
• Line/Series: Otsuka Lotec numbered model series (No.5 / No.6 / No.7.5 / No.8 / No.9)
• Origin: Japan
• Material: 316L stainless steel; hairline brushed and sandblasted industrial finish
• Size: Diameter 40 mm · Thickness 11.2 mm (max 14.8 mm) · Lug width 20 mm
• Movement: Miyota 82S5 automatic base with proprietary Otsuka Lotec jumping hour module; 24 jewels; 21,600 vibrations/hour; power reserve approx. 40 hours
• Functions: Jumping hour, minute disc, seconds disc
• Crystal: Sapphire with anti-reflective coating; sapphire fisheye lens for disc magnification
• Caseback: Exhibition sapphire caseback
• Water Resistance: Daily-life resistant
• Strap: Calf leather
• Included: Box, documents, strap and tags

Condition

Japonista grade S · Unworn or as new, complete with original packaging.

• New and unused condition, observed in hand.
• Full set with box, documents, strap and tags.

Otsuka Lotec Atelier

Otsuka Lotec was founded in Tokyo by the designer and engineer Jiro Katayama, who came to watchmaking through industrial design, metalworking and a fascination with mechanical instruments rather than a Swiss apprenticeship. His founding idea was that a wristwatch could be treated as a miniature instrument whose architecture, materials and motion communicate time with the clarity of a scientific tool. Brushed plates, exposed screws, engraved scales, retrograde arcs and layered mechanical structures make the dial read like a laboratory gauge, an aviation instrument or a mechanical dashboard.

Models are identified by number rather than name; the No.5 Kai, No.6, No.7.5, No.8 and No.9 trace the evolution of Katayama's design language. Production is small-scale and atelier-like, often distributed in restricted quantities through lotteries or tightly controlled releases within Japan, and the watches typically combine reliable Japanese mechanical base movements with proprietary display modules of Katayama's design.

Authenticity & Care

Complete with the maker's box, documents and tags; base caliber Miyota 82S5 with Otsuka Lotec's proprietary jumping hour module. Every piece is examined and documented in Japan before dispatch and is offered with the Japonista authenticity guarantee.

Delivery from Japan

Packed by hand in Japan and shipped insured and tracked by EMS or an equivalent express service. Import duties and taxes, where applicable, are payable on arrival. Returns follow our published policy.

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