Condition: This example from my collection is in great condition - everything is working perfectly; the flyback function, the stop/start function, and the crown operate quick set. The original crystal is in good condition with a few minor marks. The dial remains immaculate, free from any signs of deterioration. The original dial and hands are vibrant and intact, with no indications of decay. The transparent caseback shows minor scratches but is in great condition. The bracelet is aftermarket but looks great. History: One of the most fascinating aspects of the rivalry between Seiko’s Suwa and Daini divisions was their battle for chronograph supremacy. While vintage enthusiasts often focus on Suwa’s iconic 613X chronographs, Daini’s response with the 701X series was equally impressive, and in some ways, ahead of its time. A standout from this era is Daini's Time Sonar Ref. 7015-6010 which was introduced in 1976. Inspired by submarine sonar displays, it features a distinctive transparent dial that reveals the calendar disk beneath. The Time Sonar perfectly captures the futuristic design of the 1970s as interpreted by Japanese watchmaking: Its translucent dial showcases the quick-set calendar mechanism, making it a truly unique piece in the world of vintage chronographs. Adding to its allure is the 'smoked' display case back, offering a glimpse of its iconic Cal.7015A making it one of the first mass-produced wristwatches to feature such a display. Specifications: DIAL: Original transparent brown CASE MATERIAL: Stainless Steel CASE DIMENSIONS: 38 x 43 mm diameter, 14mm Height, 18mm Lug Width CRYSTAL: Mineral glass CASE BACK: Screw-in Stainless Steel MOVEMENT: Cal.7015A (Self-Winding) Manufacturing date: 1976 Service History: Unknown, ±10s/day Price £700 (shipping included) via PayPal F&F. Not looking for trades.