I'm rather surprised you haven't had an answer to your question! Perhaps that means that others are like me- no answer, but are reluctant to guess! So here goes, with a guess! Wrist watches began to pop up in railroad service during the early 1960s, but the early ones were Hamilton Electric (shudder), Bulova Accutron 214 and 218, and perhaps a few transistorized ones of the balance wheel type. Then along came the mechanicals such as the Ball Trainmaster, the Elgin B W Raymond, the Cyma, Longines, UG, Zenith, etc. Then the early quartz ones began to pop up, likely in the early 1970s, once they had proven themselves. So, the way I read it, yours would likely be from a 10 year span from, say 1962 to 1972. Anyone care to try to be more specific? The crystal? Plastic! Definitely plastic. Watch styles then required high dome crystals in order to clear the seconds hand. Plastic would likely be about all that would have been available at the time.