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An advantage I've found of keeping error plots (alas not for a Hamilton) is that while the rate at which the clock gains or loses time may be consistent during the cold and/or hot months, changes such as temperature seem to encourage changes in rate.

Something to bear in mind when the time-piece gets removed from its usual home and is then expected to perform in another quite different environment - such as below decks while being tossed around (along with everything else) and enduring perhaps extreme temperature variations.

Just as others have found, the best all-round chronometer (as it is that accurate) I have is an inexpensive Casio wrist-watch with a stop-watch function (useful for timing sights).