Congrats! An iconic vintage Seiko, hard to find these days at a decent price.
And Yours is from 1977, the year when this model was launched, as one may read in the Doensen's Book - WATCH. History of the modern wrist watch:
"1977 The first digital LCD 'Dual Zone Timer' by Seiko, (cal. 0139) and the 'Quartz LC World Timer' M158A, equipped to show the time in 29 different time zones, is produced."
https://doensen.home.xs4all.nl/q4.html
A nice catch indeed!
Regards,