Original vintage 1979 Seiko A239 World Time Alarm chronograph watch advertisement - "Oh, I Can See the Time Difference!"
 
Dimensions: Roughly 8 inches wide by 11 inches high - for sale is first advert only
 
In Kanji Japanese - "The 1980s are in sight.  In the future, business and leisure will become increasingly global in scale.  The Seiko World Time is the watch for this new era.  It is a digital watch that is indispensable in an international society" 
 
Seiko’s iconic A239 World Timer is a great example of how a dual-layer LCD can give a watch so much more functionality at the press of a button. 
 
Debuting in 1979, the A239 was the first watch ever produced with a dual-layer LCD screen, with two LCD panels on top of one another, which it uses to show a world map. Switching between the two has the effect of completely changing the display; the first panel shows normal time and date, and the second has a world map wherein different time zones can be selected.
 
World Time watches, even Seiko’s own M158 (Pan Am) and A708, usually relied on having a small marker (like the size of the day indicator on many LCD watches) appear at various points around the display to indicate the time in a particular city/country/zone.
 
The A239 went one better by putting a world map on a separate LCD, split into sections which lined up with the country or time zone being indicated. It offered the option for a daily alarm, as well as a separate world time alarm.
 
Although the A239 was copied and pirated, and became the World Time Melody Alarm watch for low-cost distributors Armitron, Caravelle, Zeon and others, its popularity never waned.  The A239 did not have a direct predecessor or successor, and is unique in the line of digital World Time watches from the storied Japanese watch manufacturer.