I found that the Mr. Dillon, who first worked on this watch, lived in D. C. in 1860 but later showed up on the New York census of 1870. Maybe that is why President Lincoln went to somebody else, and had to use Mr. Walter in Baltimore to work on his watch in 1864; Mr. Dillon had left. Mr. Walter was in Baltimore in 1856 with his business and still there in 1879 so its a very big possibility this is correct and Louis Edward Gross worked on this watch.

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David Upton