6M23

Very rare Seiko Space Navigator.
(This model was used by a Japanese Astronaut on one of the shuttle missions.)

Orbital Rule on the bezel
Time Indication: 3 Hands, 24-hour hand and mode indicator
Alarm function (24-hour indication system)
Stopwatch function (Up to 32 days): Measures in 1/10 second increments for the first 60 minutes.
Automatic calendar (Year, month and date up to the year 2099)
Dual time function
Hands 0-reset adjustment function (Including date position adjustment)
Alarm test sound
Confirmation sound for stopwatch function
Electronic circuit reset switch
Battery life indicator