Otsuka Lotec Nr. 5 Kai

The satellite hour watch features rotating numeral disks that orbit like satellites, combined with fixed markers to indicate the time. It has a MIYOTA movement with an in-house satellite hour module. To prevent the backlash characteristic of the satellite hour mechanism, the hour disk is driven by a double reduction gear. Additionally, to highlight the static satellite hour mechanism, careful design has been utilized to ensure the movement of the mechanics is clearly visible.

First, the hour disk directly engages with a ball bearing roller at the 8 o'clock position, allowing for instantaneous switching twice per hour, similar to a jumping hour mechanism. The seconds disk at the 5 o'clock position constantly moves regardless of the hour disk's position, providing a continuous view of its mechanism.

To emphasize the three-dimensional shape of the satellite hour mechanism, a high-profile box sapphire crystal is used, with the case edge lowered to the maximum extent. The case thickness is 7.6 mm, while the height of the box sapphire crystal is 4.6 mm. Each component housed within the sapphire crystal, including the “minute index plate” and “hour disk”, is designed to cast distinct shadows.

The No.5 KAI inherits the design elements of the No.5, which was released in 2012. The case has also been refined based on the No.5. The original No.5 used two ball bearings, and the No.5 KAI also continues to use two Japan-made ball bearings from MinebeaMitsumi. The ball bearing used for switching the hour disk was specially made for the No.5 KAI. Furthermore, the ball bearing at the center of the seconds disk was introduced in 2015 and is still the world's smallest 1.5 mm diameter as of 2025.

Originally, the Satellite hour mechanism was designed for night clocks to consolidate the hour and minute display at the top of the dial due to visual constraints, the satellite hour mechanism has been adapted in No.5 KAI to address the visual limitations of modern watches—specifically, the issue of part of the watch dial being obscured by a jacket cuff. The revised mechanism consolidates the hour and minute display on the right side of the dial, achieving a better balance and harmonious design.

Technical specifications

Ōtsuka Lōtec Nr. 5 Kai

Limited production, available only in Japan

Case

• Material: Stainless steel (316L)
• Diameter: 40.5 mm
• Thickness: 7.6 mm (Including the crystal: 12.2 mm)
• Case finish: Straight graining
• Glass: Sapphire crystal with anti-reflecting and anti-fingerprint coating)
• Case-back: Screwed
• Water-resistant to 3 ATM (~30 meters)

Dial and hands

• Openworked dial

Movement

• MIYOTA 90S5 and In-house satellite hour module
• Automatic movement
• Number of jewels: 25
• Frequency: 28,800 vph (4 hz)
• Power reserve: approximately 40 hours

Functions/Indications

• Satellite hours and minutes
• Seconds disk

Strap and buckle

• Calfskin leather strap
• Lug width: 22 mm

MSRP: JPY 748'000 (incl. taxes)

For more information, please visit otsuka-lotec.com