Heritage Spring Drive

Grand Seiko's Heritage Spring Drive watches combine familiar automatic-watch construction with a different way of keeping time. They have a mainspring, gears and a winding rotor. What they do not have is the swinging balance wheel that regulates an ordinary mechanical watch.

Instead, the spring drives a small generator as well as the hands. The electricity powers a quartz crystal and a circuit, which control an electromagnetic brake. That brake keeps a wheel turning at a steady speed. No battery powers the watch, and no electric motor steps the hands forward.

The visible consequence is the seconds hand. It glides continuously, rather than making the small repeated advances of a conventional mechanical watch or the one-second jumps common to quartz watches. It is also a useful way to distinguish two Grand Seikos that might otherwise look similar.

Spring Drive first reached Grand Seiko in 2004 with the automatic 9R65. That movement powers both the Snowflake and Shunbun in this collection. It has a date and approximately three days of running reserve when fully wound. The small gauge on the dial shows how much of that reserve remains.

Those two watches are not the same case with different dials. The Snowflake is a 41-millimeter design with a distinct ring around the glass. The 40-millimeter Shunbun uses the angular, bezel-free outline derived from the 1967 62GS. Both use titanium, but their shapes give the same movement a different setting.

The power-reserve display is the visual compromise. It makes the mechanism's remaining energy easy to read, but it also takes space from the textured dial. Grand Seiko leaves that information in view rather than making either watch a completely uninterrupted picture.