Roman numerals on an upper arm

The chronometer came back from Liverpool on Tuesday with its face scrubbed clean, and the old man at the instrument shop had written the numbers out for me on a card in pencil, because he said the figures on the dial had worn to nothing after thirty years of salt. I have copied them below so you can see. XIX, then a small gap, then the others he could not make out at all. He thought the maker meant them as a sum but he wasn't sure whose sum it was.

I have been turning it over since we left the Bight. The second mate says a chronometer keeps Greenwich in a brass box, so that a man far out can still know what hour it is at home. That is the whole trick of it. Carry one bit of England with you and you can always work out where you are against it. I told him I had never thought of a clock as a kind of homesickness, and he laughed and said that was the only sort worth keeping.

Mr Pryce wants it back in the cabin by noon for the sights, so I must be quick. When the last of the numbers stops making sense to me I shall simply wind it and count the hours, the way you did with the kitchen clock when Father was late off the boats. I still hear it sometimes, tick after tick under the floorboards at Hoylake.

Write soon. Tell Mam the tea reached me in Valparaíso, and that I am keeping the tin shut until the next port.

Your brother, Tom