Vintage Seiko Grand Quartz watch 9943-8010 Brushed dial 1978 Serviced Warranty

TWIN QUARTZ Twin Quartz is Seiko’s temperature-compensated quartz system, introduced in the late 1970s. Unlike standard quartz watches that use a single quartz crystal, Twin Quartz uses two crystals along with a specialized circuit that compares their oscillations and corrects for temperature-related timing errors.