The Seiko 66A is an open face calibre watch movement featuring a stop function with a pillar wheel. It is commonly believed to have been manufactured by Valjoux but is frequently listed in catalogs solely as Seiko 66A. The movement offers several functions, including a timer with 60s (0.2s) and 30min capabilities, controlled by the pillar wheel. Additionally, there is an optional setting for 30s (0.1s) and 15min intervals. The Seiko 66A movement is designed for stem winding and features a sweep second hand.