Thin-o-matic was used to distinguish automatic movements from those that were manually wound. This watch is a DATELINE model....specifically, a DATELINE T-277. It was around this time that Hamilton started getting away from using men's and women's first names for models and just went with standardized model designations such as Dateline, Lord / Lady Lancaster, Accumatic, Thinline, etc.
It debuted in 1964 and was offered until 1966 (maybe 1967). It was gone from the 1968 catalog.
The MSRP was $140 according to the Hamilton salesmen's '64 catalog.
Quite a dip into the ol' savings account for just a wrist watch!
Use your favorite inflation calculator to find out the buying power of that amount in 2018 dollars.